AMERICAN  SCIENCE  SERIES,   BRIEFER  COURSE^^ 


AN  INTRODUCTION  TO  THE    STUDY 


OF 


CHEMISTRY 


BY 

IRA  REMSEIST 

Professor  of  Chemistry  in  the  Johns  Hopkins  University 


\ 


NEW    YORK 
HENRY    HOLT    AND    COMPANY  f 

1887 


•v    >,  »-  ., 

"•*M    ^ 


Copyright,  1886,  by 
HENRY  HOLT  &  Co. 


PREFACE. 


IN  preparing  this  book,  I  have  endeavored  to  keep  in 
mind  the  fact  that  it  is  intended  for  those  who  are  begin- 
ning the  study  of  chemistry.  Instead  of  presenting  a  large 
number  of  facts  and  thus  overburdening  the  student's 
mind,  I  have  presented  a  smaller  number  than  is  usual  in 
elementary  courses  in  chemistry;  but  I  have  been  careful  to 
select  for  treatment  such  substances  and  such  phenomena 
as  seem  to  me  best  suited  to  give  an  insight  into  the  na- 
ture of  chemical  action.  Usually  the  mind  is  not  allowed 
to  dwell  for  any  length  *  time  upon  any  one  thing  and 
thus  to  become  really  acquainted  with  it,  but  is  hurried  on 
and  is  soon  bewildered  in  the  effort  to  comprehend  what  is 
presented.  I  cannot  but  believe  that  it  is  much  better  to 
dwell  longer  on  a  few  subjects,  provided  these  subjects  are 
properly  selected. 

The  charge  is  frequently  made  that  our  elementary  text- 
books on  chemistry  are  not  scientific;  that  is  to  say,  that 
not  enough  stress  is  laid  upon  the  relations  which  exist  be- 
tween the  phenomena  considered, — the  treatment  is  not  sys- 
tematic. The  student  is  taught  a  little  about  oxygen,  a  little 
about  hydrogen,  a  little  about  nitrogen,  etc.;  and  then  a 
little  about  potassium,  a  little  about  calcium,  etc.;  and  he 
is  left  simply  to  wonder  whether  there  is  any  connection 
between  the  numerous  facts  offered  for  study.  It  must  be 
acknowledged  that  there  are  serious  difficulties  in  the  way 
of  a  purely  scientific  treatment  of  chemistry,  but  I  think 

237459 


IV  PREFACE. 

that  it  is  quite  possible  to  treat  the  subject  more  scientifi- 
cally than  is  customary,  and  thus  to  make  it  easier  of  com- 
prehension to  the  student.  I  have  made  an  effort  in  this 
direction  in  the  book  here  offered  to  the  public. 

In  teaching  chemistry,  two  mistakes  are  commonly  made. 
The  first  is  that  of  presenting  the  profoundest  theories  of 
the  science  before  the  student  is  prepared  for  them. 
Hence  they  make  little  impression  upon  his  mind,  and 
he  only  learns  to  repeat  words  about  them,  without  having 
any  real  comprehension  of  them. 

The  other  mistake  is  that  of  giving  directions  for  ex- 
periments without  making  it  clear  to  the  student  why 
they  are  performed  or  what  they  teach.  The  result  is 
that  he  sees  little  or  no  connection  between  the  subjects 
treated  in  the  text-book  and  the  things  which  he  works 
with  in  the  laboratory. 

Now,  the  first  object  of  a  course  in  science  should  be  to 
develop  a  scientific  habit  of  thought.  This  cannot  be  done 
by  mere  study  of  the  theories  of  a  science,  nor  by  hap- 
hazard experimenting.  It  can  only  be  reached  by  system- 
atic study  of  the  phenomena,  and  by  recognizing /the 
connection  between  these  phenomena  and  the  theories. 
At  the  outset  the  best  plan  is  to  study  phenomena  scien- 
tifically, and  afterwards  speculations  may  be  introduced  to 
some  extent;  though,  in  my  opinion,  it  is  better  to  keep 
these  decidedly  subordinate  in  an  elementary  course. 

At  this  day  it  is  almost  superfluous  to  emphasize  the 
great  importan  ce  of  laboratory  work  as  a  part  of  a  course 
in  chemistry.  College  authorities  and  school  boards  are 
beginning  to  recognize  the  necessity  of  this  kind  of  work 
for  the  purpose  of  securing  satisfactory  results.  A  labora- 
tory can  be  fitted,up  at  slight  cost  in  which  all  the  experi- 


PREFACE.  V 

ments  described  in  this  book  could  be  performed.  It  is 
not  necessary  to  wait  until  a  complete  laboratory  is  pro- 
vided. The  accommodations  needed  are  simple,  and 
there  can  hardly  be  a  college  or  school  which  could  not 
with  a  little  effort  secure  the  few  conveniences.  Should 
there,  however,  be  such  a  place,  the  teacher  can  at  least 
perform  the  experiments  described.  And  this  he  had  bet- 
ter do  with  not  more  than  ten  or  a  dozen  students  around 
him.  By  constantly  questioning  them,  and  getting  one  or 
another  to  help  him,  or  to  do  the  work,  fairly  satisfactory 
results  can  be  attained. 

'  If  the  students  work  in  the  laboratory,  it  is  of  prime 
importance  that  they  should  not  be  left  to  shift  for  them- 
selves. They  will  surely  acquire  bad  habits  of  work,  and 
will  generally  fail  to  understand  what  they  are  doing.  A 
thorough  system  of  questioning  and  cross-questioning  is 
necessary  in  order  that  the  work  shall  be  successful.  A 
badly  constructed  piece  of  apparatus  should  not  be  allowed, 
and  cleanliness  should  be  insisted  upon  from  the  beginning. 
The  instructor  should  be  as  watchful  in  the  laboratory  as 
in  the  recitation-room,  and  should  be  as  exacting  in  regard 
to  the  experimental  work  as  the  teacher  of  languages  is  in 
regard  to  the  words  of  a  lesson.  A  badly  performed  experi- 
ment should  be  considered  as  objectionable  as  a  bad  reci- 
tation or  a  badly  written  exercise.  When  teachers  of  chem- 
istry acquire  this  feeling,  and  work  in  this  spirit,  the  edu- 
cational value  of  laboratory  courses  will  be  greater  than  it 
frequently  is  now.  The  average  playing  with  test-tubes 
and  precipitates  is  of  questionable  benefit.  As  it  has  been 
dignified  by  the  undeserved  name  of  scientific  training,  and 
put  forward  in  place  of  the  real  thing,  many  thinking  men 
have  been  led  to  question  the  value  of  scientific  training, 


vi  PREFACE. 

and  to  adhere  to  the  old  drill  in  grammatical  forms  and 
mathematical  problems.  I  do  not  wonder  at  this,  but  I 
should  be  greatly  surprised  to  find  this  state  of  mind  con- 
tinuing after  really  good  laboratory  courses  are  provided. 
A  slovenly  laboratory  course  in  chemistry  is  a  poor  substi- 
tute for  a  well-conducted  course  in  mathematics  or  lan- 
guages. It  behooves  those  who  are  convinced  of  the  great 
advantages  to  be  derived  from  good  laboratory  courses  to 
see  to  it  that  these  courses  are  conscientiously  conducted. 

A  few  of  the  experiments  described  in  the  book  cannot 
well  be  made  by  every  student  in  the  laboratory.  These 
the  teacher  should  make  at  all  events,  and  he  should  not 
only  make  them,  but  see  to  it  that  every  detail  is  thor- 
oughly comprehended  by  the  student.  In  the  directions 
for  the  experiments  the  quantities  recommended  are  in 
some  cases  larger  than  would  be  desirable  for  each  student. 
The  proportions  being  correctly  given  in  the  book,  the 
absolute  quantities  can  be  regulated  by  the  teacher  to  suit 
the  circumstances. 

Finally,  I  invite  correspondence  from  teachers  who  may 
use  the  book,  and  who  may  experience  any  difficulty  in  its 
use.  I  shall  gladly  avail  myself  of  any  suggestion  which 
may  help  towards  making  it  more  useful. 

The  apparatus  needed  can  be  obtained  from  any  dealer 
in  chemical  wares,  and  I  have  no  doubt  that  some  of  the 
larger  houses  would  furnish  estimates  for  all  that  is  neces- 
sary for  the  purpose  of  illustrating  the  course. 

I.  R. 

BALTIMORE,  December  21,  1885. 


CONTENTS. 


CHAPTER  I. 

CHEMICAL  ACTION — ELEMENTS — COMPOUNDS — HOW  TO  STUDY 
CHEMISTRY. 

PAGE 

Introductory— Chemical  and  physical  changes — Mechanical  mix- 
tures and  chemical  compounds — Relative  weights  of  chemical 
elements  which  act  upon  one  another — Combining  weights  of 
the  elements— Law  of  multiple  proportions — Chemical  affinity 
— Summary — How  to  study  chemistry — The  elements  and 
their  symbols 1 

CHAPTER  II. 

CHEMICAL  PHENOMENA   PRESENTED  BY  OXYGEN. 

Occurrence  of  oxygen — Preparation  of  oxygen — Physical  prop- 
erties of  oxygen — Chemical  conduct  of  oxygen — Burning  in 
the  air — Combustion — Kindling  temperature— Slow  oxidation 
— Heat  of  combustion — Heat  of  decomposition — Chemical  en- 
ergy and  chemical  work — Oxides 33 

CHAPTER  III. 

HYDROGEN. 

Occurrence — Preparation  of  hydrogen — Chemical  action  caused 
by  differences  between  the  affinities  of  the  elements  for  one 
another — Physical  properties  of  hydrogen — Chemical  proper- 
ties of  hydrogen 58 


viii  CONTENTS. 

CHAPTER  IV. 

COMBINATION  OF  HYDROGEN  AND  OXYGEN — WATER. 

PAGE 

Occurrence — Formation  of  water  and  proofs  of  its  composition 
— Measurement  of  the  volume  of  a  gas — Calculation  of  the  re- 
sults obtained  in  exploding  mixtures  of  hydrogen  and  oxygen 
— Synthesis  of  water  by  passing  hydrogen  over  heated  oxides 
— Applications  of  the  heat  evolved  by  the  combination  of  hy- 
drogen and  oxygen — Properties  of  water— Uses  of  water  in 
chemistry — Solution — Ozone — Hydrogen  dioxide — Summary — 
Comparison  of  hydrogen  and  oxygen 71 

CHAPTER  V. 

CHLORINE  AND  ITS  COMPOUNDS  WITH  HYDROGEN  AND  OXYGEN. 

-Occurrence  —  Preparation  —  Properties  —  Hydrochloric  acid  — 
Properties — Analysis  of  hydrochloric  acid — Compounds  of 
chlorine  with  oxygen  and  with  hydrogen  and  oxygen — Com- 
pounds of  chlorine  with  hydrogen  and  oxygen — Compounds 
of  chlorine  and  oxygen 95 

CHAPTER  VI. 

ACIDS — BASES — NEUTRALIZATION — SALTS. 

Nomenclature  of  acids — Nomenclature  of  bases— Nomenclature 
of  salts — Acid  properties  and  oxygen 117 

CHAPTER  VII. 

NITROGEN  —  AIR. 

Preparation  of  nitrogen— Occurrence  of  nitrogen— Properties  of 
nitrogen— Other  constituents  of  air 127 

CHAPTER  VIII. 

COMPOUNDS  OF  NITROGEN   WITH  HYDROGEN  AND  OXYGEN. 

general  conditions  which  give  rise  to  the  formation  of  the  sim- 
pler compounds  of  nitrogen — Ammonia — Preparation  of  am- 
monia— Composition  of  ammonia — Relations  between  the  vol- 
umes of  combining  gases — Relations  between  the  specific 
gravities  of  gases  and  their  combining  weights — Nitric  acid — 
Preparation  of  nitric  acid— Nitrous  acid— Anhydrides— The 
oxides  of  nitrogen— Nitrous  oxide— Nitric  oxide— Nitiogen 
peroxide — Summary 137 


CONTENTS.  ix 

CHAPTER  IX. 

CARBON. 

PAGE 

Occurrence  —  Diamond — Graphite — Amorphous  carbon — Char- 
coal— Lamp-black — Bone-bhick  —  Coal  —  Diamond,  graphite, 
and  charcoal  different  forms  of  the  element  carbon — Chemical 
conduct  of  carbon 163 

CHAPTER  X. 

COMPOUNDS   OF   CARBON   WITH   HYDROGEN,    WITH   OXYGEN,    AND 
WITH  NITROGEN. 

Petroleum — Marsh  gas,  methane,  fire-damp— Ethylene,  olefiant 
gas — Acetylene— Carbon  dioxide— Preparation  of  carbon  diox- 
ide—Carbonic acid  and  carbonates — Carbon  monoxide— Illumi- 
nation, flame,  blow-pipe — Structure  of  flames — Causes  of  the 
luminosity  of  flames — Cyanogen — Hydrocyanic  acid,  prussic 
acid — Summary 176 

CHAPTER  XI. 

THEORY  IN  REGARD  TO  THE  CAUSE  OF  THE  LAWS  OF  DEFINITE 
AND  MULTIPLE  PROPORTIONS  —  ATOMIC  THEORY  —  ATOMIC 
WEIGHTS — MOLECULAR  WEIGHTS — MOLECULAR  FORMULAS. 

The  atomic  theory — Atomic  weights — How  the  relative  weights 
of  the  atoms  are  determined— Avogadro's  hypothesis — Mole- 
cules of  the  elements — Nascent  state — How  a  formula  is  deter- 
mined— Valence — Replacing  power  of  elements — Summary. . .  209 

CHAPTER  XII. 

CLASSIFICATION   OF  THE  ELEMENTS. 

Acid-forming  elements  and  base-forming  elements— Families  of 
elements 282 

CHAPTER  XIII. 

THE   CHLORINE   FAMILY  I   CHLORINE,    BROMINE,    IODINE,    FLUORINE. 

Bromine — Hydrobromic  acid — Compounds  with  hydrogen  and 
oxygen  —  Iodine  —  Hydriodic  acid  —  Fluorine — Hydrofluoric 
acid— Comparison  of  the  members  of  the  chlorine  family 236 


X  CONTENTS. 

CHAPTER   XIV. 

THE  SULPHUR  FAMILY:   SULPHUH,    SELENIUM,    TELLURIUM. 

PAGE 

Sulphur— Extraction  of  sulphur  from  its  ores — Properties — Crys- 
tallography—  Hydrogen  sulphide,  sulphuretted  hydrogen — 
Chemical  analysis — Ilydrosulphides — Compounds  of  sulphur 
with  oxygen  and  with  hydrogen  and  oxygen — Sulphur  diox- 
ide— Sulphurous  acid— Sulphuric  acid — Monobasic  and  dibasic 
acids — Acid,  normal,  and  neutral  salts — Selenium,  tellurium, 
and  their  compounds — Points  of  resemblance  between  ox}ygcn 
and  the  members  of  the  sulphur  family 247 

CHAPTER  XV. 

THE  NITROGEN  FAMILY:   NITROGEN,    PHOSPHORUS,    ARSENIC,    AND 
ANTIMONY. 

Phosphorus — Red  phosphorus — Phosphine,  phosphuretted  hydro- 
gen— Compounds  of  phosphorus  with  oxygen  and  with  hydro- 
gen and  oxygen — Orthophosphoric  or  ordinary  phosphoric 
acid — Phosphorous  acid — Arsenic  and  its  compounds — Arsine, 
arseniuretted  hydrogen  —  Arsenic  trioxide — Antimony— Stib- 
ine,  antimoniuretted  hydrogen — Antimony  as  a  base-forming 
element — General  remarks  on  the  characteristics  of  the  nitro- 
gen family— Boron — Boric  acid — Boric  anhydride 265 

CHAPTER  XVL 

THE  CARBON  FAMILY:  CARBON  AND  SILICON. 

Silicon — Silicic  acid— Silicon  dioxide,  silicic  anhydride — Com- 
parison of  carbon  and  silicon 280 

CHAPTER  XVII. 

BASE-FORMING  ELEMENTS— GENERAL   CONSIDERATIONS. 

Families  of  the  base-forming  elements — Metallic  properties — 
Classes  of  metal  derivatives— Chlorides— Oxides— Hydroxides 
— Decomposition  of  salts  by  acids  and  by  bases — Sulphides — 
Nitrates  —  Chlorates  —  Sulphates— Carbonates— Phosphates- 
Silicates .283 


CONTENTS.  Xi 

CHAPTER  XVIII. 

THE  POTASSIUM  FAMILY:  LITHIUM,  SODIUM,  POTASSIUM,  OESIUM, 
RUBIDIUM  (AMMONIUM). 

PAGE 

Potassium — Compounds  of  potassium — Potassium  iodide — Potas- 
sium hydroxide— Potassium  nitrate — Potassium  cnlorate — So- 
dium—Sodium chloride — Sodium  hydroxide — Sodium  nitrate 
Sodium  sulphate — Sodium  carbonate — Disodium  phosphate- 
Sodium  borate — Ammonium  salts — Ammonium  chloride — Am- 
monium sulphide — Ammonium  hydrosulphide — General  char- 
acteristics of  the  metals  of  the  alkalies — Flame  reactions  and 
the  spectroscope 306 

CHAPTER  XIX. 

THE  CALCIUM  FAMILY:  CALCIUM,    BARIUM,    STRONTIUM,    BERYLLIUM. 

Calcium— Calcium  chloride— Calcium  oxide — Calcium  hydrox- 
ide— Calcium  hypoclilorite — Calcium  carbonate — Calcium  sul- 
phate— Calcium  phosphate — Monocalcium  phosphate— Mortar 
—Glass 323 

CHAPTER  XX. 

THE   MAGNESIUM  FAMILY:   MAGNESIUM,    ZINC,    CADMIUM. 

Magnesium  —  Magnesium  oxide — Magnesium  chloride — Zinc — 
Zinc  oxide — Zinc  sulphate— Zinc  chloride 331 

CHAPTER  XXI. 
THE  COPPER  FAMILY:  COPPER,  MERCURY,  SILVER. 

Copper — Cuprous  and  cupric  compounds — Cuprous  oxide — Cu- 
pric  oxide  —  Copper  sulphate — Copper  sulphide — Mercury — 
Mercuric  oxide — Mercurous  chloride — Mercuric  chloride— Mer- 
curic sulphide — Silver — Silver  nitrate — The  specific  heat  of 
elements  as  a  means  of  determining  their  atomic  weights 335 

CHAPTER  XXII. 

THE  ALUMINIUM  FAMILY:  ALUMINIUM,  GALLIUM,  INDIUM,  THALLIUM, 
SCANDIUM,  YTTRIUM,  LANTHANUM,  AND  YTTERBIUM. 

Aluminium — Aluminium  oxide — Aluminium  hydroxide — Alums 
— Aluminium  silicates— Ultramarine 347 


Xll  CONTENTS. 

CHAPTER  XXIII. 

THE  IRON  FAMILY  :    IRON,  COBALT,  NICKEL. 

PAGE 

Iron — steel — Ferrous  and  ferric  compounds — Ferrous  chloride 
— Ferrous  sulphate — Iron  alum — Ferrous  oxide — Ferric  oxide 
— Ferroso  ferric  oxide— Ferric  acid — Iron  pyrites — Nickel — 
Cobalt 351 

CHAPTER  XXIV. 

MANGANESE — CHROMIUM — URANIUM — BISMUTH. 

Manganese  —  Potassium  permanganate — Chromium — Potassium 
chroma^e — Potassium  dichromate — Chrome  Alum — Uranium— 
BismutbV-Bismuth  sulphide 857 

CHAPTER  XXV. 

THE  LEAD  FAMILY:    LEAD,  TIN — PLATINUM,  GOLD. 

Lead — Lead  peroxide  —  Lead  acetate — Lead  carbonate — Tin — 
Stannous  and  stannic  compounds — Staimous  chloride— Stan- 
nic oxide — Metastannic  acid — Stannic  chloride — Stannic  sul- 
phide— Palladium,  ruthenium,  and  rhodium — Platinum,  os- 
mium, iridium,  and  gold — Platinum  chloride— Gold 865 

CHAPTER  XXVI. 

GENERAL  CONSIDERATIONS — NATURAL  GROUPS   OF   ELEMENTS — 

CONCLUSION.  376 


AN  INTRODUCTION  TO  THE  STUDY  OF  CHEMISTRY, 


CHAPTER  I. 

CHEMICAL  ACTION.— ELEMENTS.— COMPOUNDS.  —  HOW 
TO  STUDY  CHEMISTRY. 

THOSE  things  which  are  most  familiar  to  us  are  apt  to 
be  regarded  with  least  wonder  and-  to  occasion  the  least 
thought.  It  is  only  when  we  come  to  study  them  with 
care  that  we  begin  to  see  how  wonderful  they  are;  and  if 
we  study  them  in  the  proper  way,  the  more  we  study  them 
the  more  .interesting  do  they  become.  We  are  all  familiar, 
with  a  great  many  changes  which  are  taking  place  in  the 
things  around  us,  but  unless  we  have  studied  some  of  the 
natural  sciences  these  changes  make  only  a  superficial  im- 
pression on  us,  or  if  they  awaken  thought  at  all,  that 
thought  is  necessarily  indefinite  and  unsatisfactory.  Take, 
for  example,  the  changesjnciuded  under  the  head  of  fire^ 
Unless  we  have  studied  these  changes  with  care,  what  can 
we  make  of  them?  We  see  substances  destroyed  by  fire. 
They  apparently  disappear.  We  feel  the  fceat  produced  by 
the  burning.  We  know  that  this  heat  disappears,  and  we 
have  nothing  left  in  the  place  of  the  substance  which 
burned.  We  know  that  some  things  will  burn  and  others 
will  not.  This  is  about  all  we  know  unless  we  have  stud- 
ied Chemistry,  which  has  to  deal  with  all  such  changes  as 


2  INTRODUCTION  TO   CHEMISTRY. 

those  produced  by  fire.  Take,  as  another  example,  the 
rusting  of  iron.  We  all  know  that  iron  when  exposed  to 

le  air  undergoes  a  serious  change,  becoming  covered  with 
a  reddish-brown  substance  which  we  call  rust.  If  the  piece 
of  iron  is  comparatively  thin,  and  it  be  allowed  to  lie  in 
the  air  long  enough,  it  will  be  completely  changed  to  the 
reddish-brown  substance,  and  no  iron  as  such  will  be  left. 
If  the  juices  from  fruits,  as  from  apples,  be  allowed  to  stand 
in  contact  with  air  they  undergo  change^  becoming  sour, 
and  a  somewhat  similar  change  takes  place  in  milk.  If  we 
bring  a  spark  in  contact  with  jpnpowder  there  is  a  flash 
and  the  powder  disappears,  dense  smoke  appearing  in  its 
place.  Think  for  a  moment.  What  are_the  causes  __ojf 
these  remarkable  changes?  Can  we  learn  anything  about 
them  by  study?  If  we  can,  surely  the  study  is  worth  un- 
dertaking. 

In  those  changes  which  have  been  referred  to,  the  sub- 
stances changed  disappeared  as  soiclj.  After  the  fire  the 
wood  or  the  coal,  or  whatever  may  have  been  burned,  was 
no  longer  to  be  found.  The  rustedjron  is^no  longer  iron. 
The  gunpowder  after  the  flash  is  no  longer  gunpowder. 
Changes  of  this  kind  in  which  the  su/bstances  disappear  and 
something  else  is  formed  in  their  plac 


cal  changes  ,  and  CHEMISTRY  is  the  science  which  has  to 
deal  with  changes  in  the  composition  of  substances. 

There  are  many  changes  taking  jpjace  which  do  jiot  af- 
fect the  composition  of  substances.  Iron,  for  example, 
may  be  changed  in  many  ways  and  still  remain  iron.  It 
may  become  hotter  or  colder.  There  is  certainly  a  differ- 
ence between  a  hotjpiece  of  iron  and  a  coldjnece._  Its  po- 
sition may  be  changed,  or,  as  we  say,  it  may  be  moved. 
The  difference  between  a  piece  of  iron  moving  and  a  piece 


VARIOUS  CHANGES  OF  SUBSTANCES.  3 

arrest  is  ajary  wonderful  one,  though  we  are  not,  as  a  rule, 
much  impressed  by  the  difference.  The  iron  may  be  struck 
in  such  a  way  as  to  give  forth  a  sourifl.  While  giving  forth 
the  sound  its  condition  is  certainly  different  from  that  in 
which  it  does  not  give  forth  sound.  The  iron  may  be  made 
so  hot  that  it  gives  light.  When,  for  example,  it  becomes 
" red-hot"  we  can  see  it  in  a  dark  room.  It  may  further 
be  made  so  hot  that  it  gives  off  a  great  deal  of  light,  as 
when  it  is  "white-hot."  A  piece  of  iron  may  be  changed 
further  by  connecting  it  with  what  is  known  as  a  galvanic 
battery.  A  current  of  electricity  then  passes  through  it, 
and  we  can  easily  recognize  the  difference  between  a  piece 
of  iron  through  which  a  current  of  electricity  is  passing  and 
one  through  which  no  current  is  passing.  The  former 
when  brought  into  certain  liquids  will  at  once  change  their 
composition,  while  the  latter  will  produce  no  change.  Fi- 
nally, when  a  piece  of  iron  is  brought  in  contact  with  a 
piece  of  loadstone,  it  acquires  new  properties.  It  now  has 
the  power  to  attract  and  hold  to  itself  other  pieces  of  iron. 
In  all  these  cases,  then,  the  iron  is  changed,  but  it  remains 
mm.  After  the  moving  iron  comes  to  rest  it  is  exactly  the 
same  thing  that  it  was  before.  After  the  iron  which  is 
giving  forth  sound  has  ceased  to  give  forth  sound,  it  re- 
turns to  its  original  condition.  Let  the  heated  iron  alone 
and  it  cools  down,  ceasing  soon  to  give  off  light,  and  giving 
no  evidence  of  being  warm.  Remove  the  iron  from  con- 
tact with  the  galvanic  battery  and  it  loses  those  properties 
which  are  due  to  the  current  of  electricity.  In  time,  the 
iron  which  is  magnetized  by  contact  with  the  loadstone 
loses  its  magnetic  properties.  It  no  longer  has  the  power  to 
attract  other  pieces  of  jfron.  It  does  not  differ  from  ordinary 
iron.  But,  as  we  have  seen,  if  iron  has  been  changed  by  rust- 


4  INTRODUCTION  TO  CHEMISTRY. 

ing  it  is  no  longer  Jron.  It  is  another_sub8tance?  and,  no 
matter  how  long  the  rust  may  be  allowed  to  lie  unmolested,  it 
will  not  return  to  the  form  of  iron.  Iron  may,  further,  be 
changed  by  contact  with  other  substances  than  air  so  as  to 
lose  its  properties.  Strong  vinegar,  which  contains  the 
substance  known  to  chemists  as  acetic  acid,  acts  upon  iron, 
causing  it  to  lose  its  properties.  A  new  substance  is 
formed.  The  substances  known  as  muriatic  or  hydrochloric 
acid,  nitric  acid,  and  sulphuric  acid  also  act  upon  iron  and 
give  rise  to  the  formation  of  new  substances  which  have  not 
the  properties  of  iron. 

From  what  has  been  said  in  regard  to  the  kinds  of  change 
which  iron  can  undergo,  we  see  that  these  changes-  are  of 
two  kinds: 

1st.  Those  which  do  not  permanently  affect  the  iron. 

2d.  Those  which  do  permanently  affect  the  iron  and 
which  necessarily  cause  the  formation  of  new  substances 
with  properties  quite  different  from  those  which  belong  to 
the  iron.  What  is  true  of  iron  is  true  in  general  of  all 
other  substances.  We  therefore  have  two  classes  of  changes 
presented  to  us  for  study: 

1st.  Those  which  do  not  affect  the  composition  of  sub- 
stances. 

3d.  Those  which  affect  the  composition  of  substances 
and  give  rise  to  the  formation  of  new  substances  with  new 
properties. 

Changes  of  the  first  kind  are  called  physical  changes. 
Those  of  the  second  kind  are  called  chemical  changes. 

That  branch  of  knowledge  which  has  to  deal  with  physi- 
cal changes  is  known  as  PHYSICS.  And  that  which  has  to 
deal  with  chemical  changes  is  known  as  CHEMISTRY. 

Everything  that  has  to  do  with  motion,  with  heat,  light, 


RELATIONS  BETWEEN  CHANGES.  5 

sound,  electricity,  and  magnetism,  is  studied  under  the  head 
of  Physics.  Everything  that  has  to  do  with  the  composi- 
tion of  substances  and  changes  in  the  composition  is  studied 
under  the  head  of  Chemistry. 

Although  at  first  sight  these  different  kinds  of  change 
appear  to  be  quite  distinct  from  one  another,  they  are,  in 
reality,  closely  related.  If  a  body  in  motion  be  stopped 
suddenly,  it  becomes  hot.  Many  examples  of  a  similar 
transformation  of  motion  into  heat  are  familiar :  A  wire 
becomes  hot  when  hammered  on  an  anvil ;  a  coin  rubbed 
on  cloth  becomes  hot.  In  both  cases  the  cause  of  the  heat 
is  the  interference  with  the  motion.  The  hammer  is 
stopped  and  becomes  hot ;  the  coin  is  not  stopped,  but  the 
motion  is  interfered  with,  and  we  have  to  push  harder  in 
order  to  move  it  over  the  cloth  than  we  would  to  move  it 
in  the  air.  A  wire  through  which  a  current  of  electricity 
is  passing  is  heated,  and  if  the  wire  is  small  and  the  cur- 
rent strong  it  will  become  so  hot  that  it  will  give  off  light. 
Here  the  electricity  causes  heat  and  light.  Again,  we 
know  that  by  means  of  heat  we  can  produce  motion.  The 
steam-engine  is  the  best  example  of  this  kind  of  trans- 
formation. We  build  a  fire ;  this  heats  the  water  in  the 
boiler ;  the  water  is  converted  into  steam,  which  expands 
and  moves  the  piston,  and  the  motion  of  the  piston  is  the 
seat  of  all  the  complex  motions  which  are  found  in  the 
different  parts  of  the  engine.  The  train  or  the  ship  moves. 
What  moves  it  ?  Plainly,  the  heat  is  the  cause  of  the 
motion.  But  we  can  go  a  step  farther  back  and  ask  what 
causes  the  heat  ?  The  answer  is  obvious.  It  is  the  burn- 
ing of  the  fuel.  But,  in  burning,  the  composition  of  the 
fuel  is  completely  changed.  A  change  is  produced  which 
in  itself  is  not  heat.  When  a  piece  of  coal  burns,  then,  it  is 


6  INTRODUCTION  TO  CHEMISTRY. 

undergoing  a  change  in  composition,  and,  as  a  result  of  this 
change,  heat  is  produced.  The  heat  is,  therefore,  produced 
by  a  chemical  change  in  the  coal,  and  we  may  say  that  the 
motion  of  the  steam-engine  is  the  result  of  the  chemical 
change  taking  place  in  the  coal  or  wood  which,  in  burning, 
produces  the  heat. 

Just  as  in  all  ordinary  fires  we  have  heat  produced  as  a 
result  of  chemical  changes  in  the  fuel,  so  we  may  have 
chemical  changes  produced  by  heat  or  by  electricity. 

EXPERIMENT  1. — In  a  clean,  dry  test-tube  put  enough 
white  sugar  to  make  a  layer  J  to  £  an  inch   thick.     Hold 
the  tube  in  the   flame    of   a   spirit-lamp 
or    a    laboratory    burner,    as    shown    in 
Fig.  1. 

Liquids  are  given  off  and  these  con- 
dense in  the  upper  part  of  the  tube.  A 
black  mass,  charcoal,  remains  behind. 
It  is  evident  that  a  change  in  composi- 
tion has  been  effected.  There  is  no  sugar 
left.  In  place  of  the  familiar,  white, 
sweet  substance  which  dissolves  in  water, 
i.  we  have  left  a  black,  tasteless  substance 

which  does  not  dissolve  in  water.  This  change  has  been 
produced  by  heat. 

EXPERIMENT  2. — From  a  piece  of  glass  tubing  of  about 
6  to  7  millimetres  (}  inch)  internal  diameter  cut  off  a 
piece  about  10  centimetres  (4  inches)  long  by  making  a 
mark  across  it  with  a  triangular  file,  and  then  seizing  it 
with  both  hands,  one  on  each  side  of  the  mark,  pulling  and 
at  the  same  time  pressing  slightly  as  if  to  break  it.  Clean 
and  dry  it,  and  hold  one  end  in  the  flame  of  a  laboratory 
burner  until  it  melts  together.  During  the  melting 


RELATIONS  BETWEEN  CHANGES.  7 

turn  the  tube  constantly  around  its  long  axis  so  that  the 
heat  may  act  uniformly  upon  it.  Put  into  it  enough  red 
oxide  of  mercury  (mercuric  oxide)  to  form  a  layer  about 
12  millimetres  (-£  inch)  thick.  Heat  the  tube  as  in  the 
last  experiment.  You  will  notice  that  the  color  of  the 
substance  is  changed,  and  after  a  time  minute  globules  of 
mercury  will  be  deposited  in  the  upper  part  of  the  tube, 
and,  on  cooling,  these  will  collect  together  and  fall  down, 
so  that  the  presence  of  the  mercury  is  readily  seen.  If 
during  the  heating  a  splinter  of  wood  which  has  a  spark 
on  the  end  be  thrust  into  the  tube,  the  spark  will  burst  into 
flame  and  the  wood  will  burn  much  more  actively  than  it 
would  in  the  air.  By  taking  it  out  of  the  tube  and  putting 
it  back  again  a  few  times,  the  difference  between  the 
burning  in  the  tube  and  out  of  it  will  be  shown  very 
clearly.  We  see  thus  that  by  heat  the  red  oxide  of  mercury 
is  changed.  We  get  in  place  of  it  mercury,  which  we 
see  in  the  tube,  and  an  invisible  substance  which  is  evidently 
in  the  tube,  as  is  shown  by  the  active  burning  of  the  wood. 
The  red  oxide  of  mercury  has  disappeared,  and  new  sub- 
stances have  appeared  in  its  place.  A  change  in  composi- 
tion has  been  effected.  Or  a  chemical  change  has  been 
caused  by  heat. 

In  a  galvanic  battery  there  are  always  substances  which 
arc  undergoing  changes  in  composition,  and  the  electric 
current  is  due  to  these  changes.  It  is  therefore  true  that 
electric  currents  are  produced  by  chemical  changes.  A 
simple  form  of  a  battery  is  represented  in  Fig.  2. 

The  plates  marked  k  are  of  copper,  those  marked  z  of 
zinc.  The  plates  are  connected  together  by  wires,  as  shown. 
In  each  vessel  there  is  poured  a  mixture  of  sulphuric  acid 
and  water.  This  mixture  acts  upon  the  zinc,  producing  a 


8 


INTRODUCTION  TO  CHEMISTRY. 


chemical  change  in  it.  This  is  the  cause  of  the  electric 
current  which  passes  through  the  wire.  As  has  already 
been  stated,  this  wire  not  only  conducts  the  electric  current, 


Fl».  2. 


but  also  becomes  heated.  Here,  then,  we  have  an  electric 
current  caused  by  chemical  change,  and  heat  caused  by  the 
electric  current. 

As  has  been  said,  an  electric  current  has  the  power  to 
cause  changes  in  composition,  or  chemical  changes.  This 
may  be  well  illustrated  by  the  action  of  a  current  on  water. 

EXPERIMENT  3. — To  the  ends  of  the  copper  wires  con- 
nected with  two  cells  of  aBunsen's  or  Grove's  battery  fasten 
small  platinum  plates  say  25  mm.  (1  inch)  long  by  12 
mm.  (£  inch)  wide.  Insert  these  platinum  electrodes  into 
water  contained  in  a  small  shallow  glass  vessel  about  15  cm. 
(6  inches)  wide  and  7  to  8  cm.  (3  inches)  deep,  taking 
care  to  keep  them  separated  from  each  other.  No  ac- 
tion will  take  place,  for  the  reason,  as  has  been  shown,  that 
water  will  not  conduct  the  current,  and  hence  when  the 
platinum  electrodes  are  kept  apart  there  really  is  no  cur- 
rent. By  adding  to  the  water  about  one  tenth  its  own 
volume  of  strong  sulphuric  acid,  it  acquires  the  power  to 
convey  the  current.  It  will  then  be  observed  that  bubbles 
rise  from  each  of  the  platinum  plates.  In  order  to  collect 
them  we  may  arrange  an  apparatus  as  shown  in  figure  3. 


CHANGES  CAUSED  BY  GALVA 


CURRENT.       9 


A  and  B  represent  glass  tubes  which  may  conveniently  be 
about  30  cm.  (1  foot)  long  and  25  mm.  (1  inch)  internal 
diameter.  They  are  first  filled  with  the  water  con- 
taining one  tenth  its  volume  of  sulphuric  acid,  and  then 
placed  with  the  mouth  under  water  in  the  vessel  C.  The 
platinum  electrodes  are  now  brought  beneath  the  inverted 
tubes.  The  bubbles  which  rise  from  them  will  pass  up- 
ward in  the  tubes  and  the  water  will  be  pressed  down. 
Gradually  the  water  will  be  completely  forced  out  of  one  of 


FIG.  3. 

the  tubes,  while  the  other  is  still  half  full  of  water.  The 
substance  which  we  have  thus  collected  in  each  of  the  tubes 
is  an  invisible  gas.  After  the  first  tube  is  full  of  gas,  remove 
it  by  placing  the  thumb  over  the  mouth.  Turn  it  mouth 
upward  and  at  once  apply  a  lighted  match  to  it.  A  flame 
will  be  noticed.  The  gas  which  was  contained  in  the  tube 
is  therefore  capable  of  burning.  It  cannot,  therefore,  have 
been  air.  In  the  mean  time  the  second  tube  will  have  become 
filled  with  gas.  Eemove  this  tube  in  the  same  way  and 
insert  a  thin  piece  of  wood  with  a  spark  on  it.  The  .spark 


10  INTRODUCTION  TO  CHEMISTRY. 

will  at  once  burst  into  flame,  and  the  burning  of  the  wood 
will  take  place  more  actively  than  it  does  in  ordinary  air. 
as  may  be  shown  by  withdrawing  it  and  again  inserting  it 
into  the  tube.  The  gas  in  this  tube,  it  will  be  noticed,  does 
not  take  fire.  Without  going  into  further  details,  it  is 
clear  from  the  above  experiment  that  when  an  electric  cur- 
rent acts  on  water  two  invisible  gases  are  produced.  We  shall 
have  occasion  hereafter  to  study  this  experiment  much 
more  carefully,  and  we  shall  find  that  from  it  we  can  learn 
a. great  deal  more  than  we  have  just  learned;  but  our  ob- 
ject now  is  to  learn  that  an  electric  current  can  produce  a 
chemical  change. 

NOTE  FOR  STUDENT. — The  method  adopted  for  collecting  the 
gases  is  apt  to  appear  somewhat  mysterious  to  the  beginner,  and 
his  attention  is  thus  drawn  away  from  the  important  part  of  the 
experiment.  It  will  on  this  account  be  well  for  the  student  to 
familiarize  himself  with  the  method  by  means  of  a  few  experiments 
especially  undertaken  for  the  purpose. 

EXPERIMENT  4.— Fill  a  test-tube  or  glass  cylinder  with 
water ;  close  the  mouth  with  the  thumb  or  a  ground-glass 
plate ;  invert  the  tube,  and  put  the  mouth  under  water. 
The  water  stays  in  the  tube  after  the  thumb  or  glass  plate 
is  removed.  (Why  ?)  Now  take  a  piece  of  glass  or  rubber 
tubing  ;  put  one  end  under  the  mouth  of  the  inverted  tube, 
and  blow  gently  through  the  other  end.  Bubbles  will  rise 
in  the  tube  a-nd  the  water  will  be  displaced.  In  this  case 
the  gases  from  the  lungs  are  collected.  When  they  come 
below  the  mouth  of  the  tube,  being  lighter  than  water,  they 
rise,  and  as  the  space  occupied  by  them  cannot  be  occupied 
by  the  water  too,  the  latter  is  displaced.  (See  Fig.  4.) 

EXPERIMENT  5. — To  transfer  a  gas  from  one  vessel  to 
another  by  displacement  of  water,  place  both  vessels  invert- 
ed in  the  same  bath,  and  then  gradually  bring  the  one  con- 


RELATIONS  BETWEEN  CHANGES.  11 

taining  the  gas  mouth  upward,  below  the  one   containing 
the  water.     (See  Fig.  5.) 
The  above  examples  will  suffice  to  prove  that  the  differ- 


FIG.  4. 


ent  kinds  of  changes,  both  physical  and  chemical,  are  more 
closely  related  to  one  another  than  they  appear  to  be  at 
first  sight.  In  consequence  of  this  relation,  we  cannot 
deal  with  chemical  changes  without  constantly  having  to 


FIG.  5. 


deal  with  physical  changes.  For  a  thorough  understand- 
ing of  chemical  changes  it  is  necessary  to  have  some  knowl- 
edge of  the  changes  produced  by  heat  and  electricity.  We 


12  INTRODUCTION  TO  CHEMISTRY. 

shall  find  that  whenever  chemical  changes  take  place,  heat 
changes  and  electric  changes  also  take  place.  And  we  shall 
find,  too,  that,  in  order  to  bring  about  chemical  changes, 
we  frequently  make  use  of  heat  and  electricity.  If,  there- 
fore, the  student  has  not  studied  physics,  he  should  famil- 
iarize himself  with  a  few  of  the  elementary  facts  of  the  sci- 
ence before  undertaking  the  study  of  chemistry.*  He 
should  know  what  physical  changes  can  be  produced  by 
heat;  what  boiling  is;  what  evaporation  is;  what  condens- 
ing a  vapor  means;  what  the  expression  "  to  pass  an  elec- 
tric current "  means;  how  the  more  common  forms  of  gal- 
yanic  batteries  are  made,  etc.,  etc.  All  these  matters  are 
of  importance  in  studying  chemical  changes,  and  still  a 
text-book  of  chemistry  is  not  the  proper  place  to  treat  them. 
It  will  therefore  be  assumed  that  the  student  has  this 
knowledge. 

Everything  that  has  to  do  with  the  composition  of  sub- 
stances is  the  object  of  the  chemist's  study.  It  is  plain  to 
every  one  that  the  number  of  substances  of  different  kinds 
found  in  nature  is  very  great,  and  the  study  of  their  com- 
position appears  to  be  an  almost  hopeless  task;  but  the 
more  we  learn  about  them  the  more  systematic  our  knowl- 
edge will  become,  and  although  the  number  of  substances 
is  large  and  they  present  a  great  variety  of  properties,  still 
the  subject  is  not  in  reality  so  difficult  as  it  seems.  Most 
of  the  substances  we  meet  with  can  by  proper  methods  be 
separated  into  simpler  ones,  and  these  again  into  still  sim- 
pler ones  which  cannot  be  further  decomposed  by  any 
means  known  to  us.  Such  substances  as  cannot  be  decom- 

*  A  simple  book  which  treats  of  the  essential  elementary  facts  of 
physics  is  Balfour  Stewart's  ' '  Primer  of  Physics. "  It  is  well  worth  a 
careful  study. 


MIXTURES  AND  COMPOUNDS.  13 

posed  into  simpler  ones  by  us  are  called Clements.  Now. 
although  there  are  thousands  and  thousands  of  different 
kinds  of  substances  met  with  in  nature,  these  are  really 
made  up  of  a  comparatively  small  number  of  simple  sub- 
stances or  elements.  The  number  of  elenients  thus  far 
discovered  is  between  sixty  and  seventy,  but  the  larger  num- 
ber of  these  are  rare,  and  we  might  have  a  very  excellent 
knowledge  of  the  essentials  of  chemistry  without  any 
knowledge  of  these  rare  elements.  We  shall  find  that  most 
things  we  have  to  deal  with  are  really  made  up  of  about  a 
dozen  elements,  and  that  most  of  the  chemical  changes 
which  are  taking  place  around  us,  and  which  we  need  to 
study  in  order  to  get  an  insight  into  the  nature  of  chemical 
action,  take  place  between  this  small  number  of  elements. 
In  studying  the  principles  of  astronomy  it  is  not  necessary 
to  consider  every  known  heavenly  body;  and  in  studying 
the  essentials  of  zoology  it  is  not  necessary  to  study  every 
known  animal.  So,  also,  in  studying  the  essentials  of  chem- 
istry it  is  not  necessary  to  study  all  known  substances. 
We  should  rather  endeavor  at  first  to  select  such  substances 
and  such  examples  of  their  action  upon  one  another  as  are 
of  fundamental  importance,  and  study  these  with  some 
care.  By  so  doing  we  shall  get  a  really  better  knowledge 
of  chemical  substances  and.  chemical  changes  than  we 
should  by  studying  more  superficially  a  larger  number  of 
substances  and  changes. 

Mechanical  Mixtures  and  Chemical  Compounds. — Most  of 
the  substances  found  in  nature  are  made  up  of  several 
others.  Wood,  for  example,  is  very  complex,  containing 
a  large  number  of  distinct  substances  intimately  mixed  to- 
gether. Some  of  these  can  be  isolated,  but  it  is  impossible 
to  isolate  them  all  with  the  means  at  present  at  our  com- 


14  INTRODUCTION  TO  CHEMISTRY. 

mand.  Most  of  the  rocks  met  with  are  also  quite  complex, 
and  it  is  a  difficult  matter  to  isolate  the  constituents.  If 
we  look  at  a  piece  of  coarse-grained  granite  we  see  plainly 
enough  that  it  con  tains  different  things  mixed  together,  and 
if  it  be  broken  up  we  can  pick  out  pieces  of  different  sub- 
stances from  the  mass.  If  we  now  examine  a  piece  of  each 
of  the  different  substances  thus  picked  out  of  the  granite, 
it  appears  to  be  homogeneous,  i.e.,  we  cannot  recognize 
the  presence  of  more  than  one  kind  of  thing  in  any  one 
piece.  If  the  piece  is  carefully  selected  it  may  be  powdered 
finely  in  an  agate  mortar,  and  some  of  the  powder  examined 
with  a  microscope  without  the  presence  of  more  than  one 
substance  being  recognized.  We  are  able  to  isolate  three 
substances  from  granite  by  simply  breaking  it  up  and  pick- 
ing out  pieces  of  different  kinds.  We  might  therefore  con- 
clude that  granite  consists  of  three  substances.  This  is 
true,  but  it  is  not  the  whole  truth.  For  it  is  possible  by 
proper  means  to  get  simpler  substances  from  each  of  the 
three  already  separated.  This,  however,  is  a  much  more 
difficult  process  than  the  separation  first  accomplished.  To 
effect  the  separation  of  each  of  the  three  constituents  of 
granite  into  its  elements  requires  more  powerful  means. 
Substances  must  be  brought  in  contact  with  them  which 
act  upon  them,  changing  their  composition,  i.  e.,  act  chem- 
ically upon  them,  and  high  heat  must  be  used  to  aid  the 
action.  By  hard  and  skilful  work  it  is  possible  to  separate 
the  three  components  of  granite  into  their  elements. 

EXPEEIMENT  6. — The  teacher  should  provide  a  piece  of 
coarse-grained  granite,  and  ask  the  students  to  separate  the 
three  components  and  to  note  the  differences  between  them. 
One  of  the  pieces  should  then  be  pulverized  and  some  of 
the  powder  put  on  the  slide  of  a  microscope,  and  each  stu- 
dent asked  to  examine  the  powder. 


MIXTURES  AND  COMPOUNDS.  15 

From  the  above  observations  and  statements  we  see  that 
substances  may  be  united  in  different  ways.  They  may  be 
so  united  that  it  is  a  simple  thing  to  separate  them  by 
mechanical  processes.  Or  they  may  be  so  united  that  it  is 
impossible  to  separate  them  by  mechanical  processes.  By 
a  mechanical  process  is  meant  any  process  which  does  not 
involve  the  use  of  heat,  electricity,  or  chemical  change. 
Thus,  the  mechanical  process  made  use  of  in  the  case  of 
granite  consisted  in  picking  out  the  pieces.  The  separa- 
tion of  particles  of  different  sizes  by  means  of  a  sieve  is  a 
mechanical  process.  The  separation  of  two  liquids  which 
do  not  mix  with  each  other  is  a  mechanical  process.  If 
we  rub  together  in  a  mortar  a  little  sulphur  and  iron  filings, 
it  makes  no  difference  how  intimately  we  may  mix  them, 
they  remain  iron  and  sulphur.  The  mixture  may  appear 
to  the  naked  eye  to  be  homogeneous,  but  the  microscope 
will  show  the  particles  of  iron  lying  side  by  side  with  the 
particles  of  sulphur. 

EXPEEIMENT  7. — Mix  a  gram  or  two  of  powdered  roll- 
sulphur  and  an  equal  weight  of  very  fine  iron  filings  in  a 
small  mortar.  Examine  a  little  of  the  mixture  with  a 
microscope. 

Not  only  can  we  recognize  the  particles  of  iron  and  of 
sulphur  by  means  of  the  microscope,  but  we  can  also  pick 
out  the  pieces  of  iron  by  means  of  a  magnet.  The  magnet 
attracts  the  iron  but  not  the  sulphur,  so  that  by  passing 
the  magnet  often  enough  through  the  mixture  we  can  pick 
out  all  the  iron  and  leave  all  the  sulphur.  This  separation 
is  really  a  mechanical  separation.  It  is  only  a  somewhat 
more  refined  method  of  picking  out  than  that  used  in  the 
case  of  granite. 

EXPEEIMENT  8. — Pass  a  small  magnet  through  the  mix- 


16  INTRODUCTION  TO   CHEMISTRY. 

ture  above  prepared.  Unless  the  substances  used  are 
thoroughly  dry,  particles  of  sulphur  will  adhere  to  the  mag- 
net, but  even  then  it  will  be  seen  that  most  of  that  which 
is  taken  out  of  the  mixture  is  iron. 

The  iron  and  sulphur  may  also  be  separated  by  treating 
the  mixture  with  a  liquid  known  as  bisulphide  of  carbon. 
Sulphur  dissolves  in  this  liquid,  but  iron  does  not.  So 
that  when  the  mixture  is  treated  with  it  the  iron  is  left  be- 
hind, and  can  easily  be  recognized  as  such. 

EXPERIMENT  9. — Pour  two  or  three  cubic  centimetres 
of  bisulphide  of  carbon  on  a  little  powdered  roll-sulphur 
in  a  dry  test-tube.  The  sulphur  dissolves.  Treat  iron  . 
filings  in  the  same  way.  The  iron  does  not  dissolve.  Now 
treat  a  small  quantity  of  the  mixture  with  bisulphide  of 
carbon.  After  the  sulphur  is  dissolved  pour  off  the  solution 
on  a  good-sized  watch  glass  and  let  it  stand.  Examine 
what  remains  undissolved  in  the  test-tube  and  satisfy  your- 
self that  it  is  iron.  After  the  liquid  has  evaporated  examine 
what  is  left  in  the  watch  glass  and  satisfy  yourself  that  it 
is  sulphur.  Why  are  you  justified  in  concluding  that  the 
substance  left  in  the  test-tube  is  iron  and  that  left  on  the 
watch  glass  is  sulphur? 

The  mixture  of  iron  and  sulphur  with  which  we  have 
been  experimenting  is  a  mechanical  mixture.  It  contains 
iron  and  sulphur  as  such.  The  iron  is  attracted  by  the  mag- 
net, just  as  if  the  sulphur  were  not  present.  The  sulphur 
burns,  just  as  if  the  iron  were  not  present.  The  sulphur 
further  dissolves  in  bisulphide  of  carbon,  just  as  if  the 
iron  were  not  present.  The  mixture  possesses  the  proper- 
ties of  both  of  its  constituents. 

We  may  allow  the  mixture  of  sulphur  and  iron  to  lie  for 
any  length  of  time,  and  it  will  remain  simply  a  mechanical 


CHEMICAL  ACTION.  17 

mixture.  If,  however,  we  put  it  in  a  test-tube  and  heat  it, 
a  remarkable  change  takes  place.  At  first  the  sulphur 
melts  and  becomes  dark-colored.  It  may  even  take  fire. 
But  soon  something  else  evidently  takes  place.  The  whole 
mass  begins  to  glow,  and  if  we  at  once  take  the  tube  out 
of  the  flame,  the  mass  continues  to  glow,  becoming  brighter. 
This  soon  stops;  the  mass  grows  dark  and  gradually  cools 
down.  As  soon  as  it  reaches  the  ordinary  temperature,  the 
tube  should  be  broken  and  the  contents  put  in  a  mortar. 
A  close  examination  will  show  that  the  mass  does  not  look 
like  the  mixture  of  sulphur  and  iron  with  which  we  started. 
It  has  a  bluish-black  color  and  is  apparently  homogeneous. 
An  examination  with  the  microscope,  the  magnet  and 
bisulphide  of  carbon  will  prove  that,  while  there  may  be  a 
little  iron  left,  and  possibly  a  little  sulphur,  most  of  the 
bluish-black  mass  is  neither  iron  nor  sulphur,  but  a  new 
substance  with  properties  quite  different  from  those  of  iron 
and  from  those  of  sulphur. 

EXPERIMENT  10. — For  the  purpose  of  'the  experiments 
just  described  make  a  fresh  mixture  of  three  grams  each  of 
powdered  roll-sulphur  and  fine  iron  filings.  Grind  them 
together  very  intimately  in  a  dry  mortar  and  put  them  in 
a  dry  test-tube.  Heat  until  the  mass  begins  to  glow. 

The  new  substance  formed  as  the  result  of  the  action  of 
the  sulphur  and  iron  upon  each  other  is  no  longer  a  me^ 
chanical  mixture.  We  cannot  decompose  it  by  a  mechani- 
caTprocess.  The  constituents  are  much  more  firmly  united 
than  they  were  in  the  mixture.  They  have  lost  their 
identity.^  They  are  both  present,  to  be  sure,  but  by  means 
of  any  ordinary  examination  we  cannot  recognize  them,  as 
their  properties  have  been  lost.  When  the  mixture  began 
to  glow,  the  act  of  combination  began,  an4  the  glowing 


18  INTRODUCTION  TO  CHEMISTRY. 

was  a  result  of  the  act  of  combination.  The  sulphur,  and 
iron  combined  with  each  other  chemically,  and  formed  a 
chemical  compound.  They  did  not  act  upon  each  other 
when  simply  brought  in  contact.  It  was  necessary  to^  heat 
the  mixture  in  order  to  cause  chemical  combination  to  take 
place.  The  heat  in  this  case  helped  the  chemical  action. 
But  after  the  action  began  it  continued  without  further  aid 
and  produced  heat^as  was  shown  by  the  glowing  of  the  mass. 

The  essential  feature  of  the  action  in  the  case  of  iron  and 
sulphur,  just  discussed,  is  this:  that  the  substances  which 
act  upon  each  other_lose  their  own  properties  and  some- 
thing is  formed  with  entirely  new  properties.  This  is  true 
of  every  case  of  chemical  action,  and  it  is  one  of  the  chief 
characteristics  of  that  kind  of  action.  If  we  should  exam- 
ine a  number  of  cases  of  chemical  action,  we  might  be  in- 
clined to  think  that  they  had  no  common  features;  but 
this  loss  of  properties  and  the  formation  of  new  substances 
always  take  place.  A  few  examples  will  help  to  show  the 
truth  of  this  statement. 

EXPERIMENT  11. — Examine  a  piece  of  calc-spar  or  mar- 
ble. You  see  that  it  is  made  up  of  pieces  of  definite  shape. 
It  is,  as  we  say,  crystallized.  It  is  quite  hard,  though  a 
knife  will  cut  it.  Heated  in  a  small  glass  tube,  as  in  Ex- 
periment 2,  it  does  not  melt,  but  remains  essentially  un- 
changed. It  does  not  dissolve  in  water.  To  prove  this, 
put  a  piece  the  size  of  a  pea  in  a  test-tube  with  pure  water. 
Thoroughly  shake,  and  then,  as  heating  usually  aids  so- 
lution, boil.  Now  pour  off  a  few  drops  of  the  liquid  on  a 
piece  of  platinum*  foil  or  a  watch  glass,  and  by  gently  heat- 

*  Platinum  an  expensive  metal,  finds  extensive  us«  in  chemical 
laboratories,  for  the  reason  that  it  resists  the  action  of  heat  and  of 
roost  chemical  substances. 


CHEMICAL  ACTION.  19 

ing  cause  the  water  to  evaporate.  If  there  is  anything 
solid  in  solution  there  will  be  a  residue  on  the  platinum 
foil  or  watch  glass.  If  not,  there  will  be  no  residue.  Now 
treat  a  small_piece  of  the  substance  with  dilute  hydrochloric 
acid  and  notice  what  takes  place.  Babbles  of  gas  are  given 
off.  After  the  action  has  continued  for  about  a  minute, 
insert  a  lighted  match  in  the  upper  part  of  the  tube.  It  is 
extinguished  and  the  gas  does  not  burn.  The  gas  formed 
in  this  case  is  therefore  plainly  not  identical  with  either 
one  of  those  obtained  from  water  by  the  action  of  the  elec- 
tric current  (see  Experiment  3).  It  is  what  is  commonly 
called  carbonic  acid  gas.  As  the  action  continues  the  piece 
of  calc-spar  or  marble  grows  smaller  and  smaller  and  finally 
disappears,  when  we  have  a  clear  solution.  The  substance 
has  dissolved  in  the  hydrochloric  acid.  In  order  to  deter- 
mine whether  anything  else  has  taken  place  besides  the  dis- 
solving, we  shall  have  to  get  rid  of  the  excess  of  hydrochlo- 
ric acid.  This  we  can  easily  do  by  boiling  it,  when  it  passes 
off  in  the  form  of  vapor,  and  then  whatever  is  in  solution 
will  remain  behind.  For  this  purpose  put  the  solution  in 
a  small,  clean  porcelain  evaporating-dish,  and  put  this  on  a 
vessel  containing  boiling  water,  or  a  water-bath.  The  op- 
eration should  be  carried  on  in  a  place  in  which  the  draught 
is  good,  so  that  the  vapors  will  not  collect  in  the  working- 
room.  They  are  not  poisonous,  but  they  are  annoying.  The 
arrangement  for  evaporating  is  represented  in  Fig.  6. 

After  the  liquid  has  evaporated  and  the  substance  in  the 
evaporating-dish  is  dry,  examine  it  and  carefully  compare  its 
properties  with  those  of  the  substance  which  was  put  into 
the  test-tube.  Its  structure  will  be  found  not  to  present 
the  regularities  noticed  in  the  original  substance.  It  is 
much  softer.  It  dissolves  in  water.  It  melts  when  heated 


20  INTRODUCTION  TO  CHEMISTRY. 

in  a  tube.  It  does  not  give  off  a  gas  when  treated  with  hy- 
drochloric acid.  When  exposed  to  the  air  it  soon  becomes 
moist,  and  after  a  time  liquid.  The  experiment  shows  us 
that  when  hydrochloric  acid  acts  upon  calc-spar  or  marble, 

the  latter  at  least  loses  its  own 
properties.  It  might  be  shown 
that  some  of.  the  hydrochlo- 
ric acid  also  loses  its  proper- 
ties. In  place  of  the  two  we 
get  a  new  substance  with  en- 
tirely different  properties. 
The  two  substances  have  acted 
chemically  upon  each  other 
and  produced  a  chemical  com- 
pound. In  this  case  it  was 
FlG-6-  only  necessary  to  bring  the 

substances  in  contact  in  order  to  cause  them  to  act  chemi- 
cally upon  each  other.  It  was  not  necessary  to  heat  them, 
as  it  was  in  the  case  of  the  iron  and  sulphur. 

EXPERIMENT  12. — Bring  together  in  a  test-tube  a  small 
piece  of  copper  and  some  moderately  dilute  nitric  acid.  In 
a  short  time  action  begins.  The  upper  part  of  the  tube 
becomes  filled  with  a  dark,  reddish-brown  colored  gas 
which  has  a  disagreeable  smell.  Do  not  inhale  it,  as  when 
taken  into  the  lungs  it  produces  bad  effects.  The  solution 
becomes  colored  dark  blue,  and  the  copper  disappears. 
Examine  this  solution,  as  in  Experiment  9,  and  see  what  has 
been  formed.  What  are  the  properties  of  the  substance 
found  after  evaporation  of  the  liquid?  Is  it  colored? 
Is  it  soluble  in  water?  Does  it  change  when  heated  in  a  tube? 
Is  it  hard  or  soft?  Does  it  in  any  way  suggest  the  copper 
with  which  we  started? 


CHEMICAL  ACTION.  21 

EXPERIMENT  13.— Try  the  action  of  dilute  sulphuric 
acid  on  a  little  zinc  in  a  test-tube.  A  gas  will  be  given  off. 
Apply  a  lighted  match  to  it.  Does  the  result  suggest  any- 
thing noticed  in  an  experiment  already  performed?  After 
the  zinc  has  disappeared  evaporate  the  solution  as  in  Experi- 
ments 9  and  10.  Carefully  compare  the  properties  of  the 
substance  left  behind  with  those  of  zinc. 

EXPERIMENT  14. — Hold  the  end  of  a  piece  of 'magnesium 
ribbon  about  20  centimetres  (8  inches)  long  in  a  flame  un- 
til it  takes  £re;  then  hold  the  burning  substance  quietly 
over  a  piece  of  dark  paper,  so  that  the  light  white  product 
may  be  collected.  Compare  the  properties  of  this  white 
product  with  those  of  the  magnesium.  Here  again  a  chem- 
ical act  has  taken  place.  The  magnesium  has  combined 
with  something  which  it  found  in  the  air,  and  heat  was 
produced  by  the  combination.  The  product  is  the  white 
substance. 

EXPEKIMENT  15. — In  a  small,  dry  flask  (400  to  500  ccm.) 
put  a  bit  of  granulated  tin.  Pour  upon  it  2  or  3  ccm. 
concentrated  nitric  acid.  If  no  change  takes  place,  heat 
gently  and  presently  there  will  be  a  copious  evolution  of  a 
reddish-brown  gas  with  a  disagreeable  smell,  (under  what 
conditions  has  a  gas  like  this  already  been  obtained?)  the 
tin  will  disappear,  and  in  its  place  will  appear  a  white  pow- 
der. Compare  the  properties  of  this  white  powder  with  those 
of  tin.  Why  are  you  justified  in  concluding  that  they  are 
not  the  same  thing? 

Experiments  like  those  just  performed  might  be  multi- 
plied indefinitely.  But  a  sufficient  number  have  already 
been  studied  to  show  upon  what  kinds  of  observations  is 
based  the  statement  that: 

Whenever  two  or  more  substances  act  upon  one  another 


22  INTRODUCTION  TO  CHEMISTRY. 

chemically  they  lose  their  own  properties,  and  new  substances 
are  formed  with  entirely  different  properties. 

Relative  Quantities  of  Chemical  Elements  which.  Act  upon 
one  Another. — A  magnet  of  a  certain  strength  will  support 
a  piece  of  iron  of  a  certain  weight.  But  it  will  also  support 
any  piece  of  iron  weighing  less.  It  shows  no  preference 
for  certain  weights  of  iron.  So,  also,  the  earth  attracts  all 
bodies,  light  or  heavy,  showing  no  preference  for  certain 
weights.  When  substances  act  upon  one  another  chemi- 
cally, however,  it  is  found  that  a  certain  weight  of  one  will 
combine  with  a  definite  weight  of  another,  and  only  with 
this  weight — no  more  and  no  less.  Take  again,  for  exam- 
ple, the  case  of  iron  and  sulphur.  If  equal  weights  of 
these  elements  be  mixed  and  caused  to  act  chemically  by 
the  aid  of  heat,  it  will  be  found  that  some  of  the  sulphur  is 
left  over  in  the  uncombined  state  after^the  action  is  over. 
If  we  should  take  twice  as  much  iron  as  sulphur,  then, 
after  the  action,  some  iron  would  be  left  over.  If  -we  were 
to  make  a  large  number  of  experiments  with  grea',  care,  we 
should  find  that  when  the  two -elements  are  mixed  in  the 
proportion  of  seven  parts  of  iron  to  four  parts  of  sulphur 
the  action  is  perfect,  neither  iron  nor  sulphur  being  left 
over.  If  we  study  other  cases  of  chemical  action  in  the 
same  way,  we  find  that  each  element  exhibits  a  tendency  to 
unite  with  others  in  quantities  which  can  always  be  ex- 
pressed by  the  same  figure.  Let  us  return  to  the  exam- 
ples already  studied.  See  Experiments  10,  14,  15.  When 
magnesium  burns  it  really  combines  with  oxygen,  as  will  be 
shown  later.  The  quantities  of  magnesium  and  oxygen 
which  combine  bear  to  each  other  the  relation  3:2.  We  can, 
of  course,  express  this  fact  by  saying  that  the  compound  of 
magnesium  and  oxygen  contains, — 


DEFINITE  COMPOSITION  OF  COMPOUNDS,         23 

Magnesium,   60  per  cent, 
and  Oxygen,  40  "      " 

When  nitric  acid  acts  upon  tin  it  gives  up  oxygen,  and 
the  white  substance  formed  is  a  compound  of  tin  and  oxy- 
gen. If  this  is  perfectly  dried  it  is  found  to  contain  tin  and 
oxygen  in  the  proportion  of  59  parts  of  tin  to  16  parts  of 
oxygen,  or  its  composition  is, — 

Tin,         78f  per  cent; 
Oxygen,  2H   "      " 

The  oxide  of  mercury,  which  was  used  in  Experiment  2, 
contains  mercury  and  oxygen  in  the  proportion  of  25  parts 
:>f  mercury  to  2  parts  of  oxygen,  or  its  composition  is, — 


Mercury,  92.59  per  cent; 
Oxygen,      7.41    "     " 


The  elements,  sulphur  and  oxygen,  unite  under  certain 
circumstances  and  form  a  compound  containing  an  equal 
weight  of  each,  or  its  composition  is, — 

Sulphur,  50  per  cent; 
Oxygen,  50   "      " 

An  extensive  examination  has  shown  conclusively  that 
each  chemical  compound  always  contains  the  same  elements 
in  exactly  the  same  proportions.  The  compound  of  sul- 
phur and  iron  always  contains  exactly  36.36  per  cent  of  sul- 
phur and  63.64  per  cent  of  iron.  The  compound  of  mag- 
nesium and  oxygen  always  contains  exactly  60  per  cent  of 
magnesium  and  40  per  cent  of  oxygen,  and  so  on  through- 
out the  list  of  chemical  elements.  These  facts  were  discov- 
ered by  the  united  efforts  of  a  large  number  of  chemists 
continued  through  several  years.  They  are  of  very  great 


24  IXTttODVCTXOft  TO  CHEMISTRY. 

importance.     They  are  summed  up  in  the  general  state- 
ment. 

Chemical  combination  always  takes  place  between  definite 
masses  of  substances. 

This  is  known  as  the  law  of  definite  proportions.  It  is 
simply  a  statement  of  what  we  have  every  reason  to  believe 
to  be  the  truth.  Every  fact  known  to  us  in  regard  to 
chemical  combination  is  in  accordance  with  this  general 
statement.  It  expresses  what  we  learn  by  a  study  of  chem- 
ical facts.  It  must  be  borne  in  mind  that  this  law,  as  well 
other  laws  governing  natural  phenomena,  can  never  be 
proved  to  be  absolutely  true,  for  the  reason  that  we  cannot 
examine  every  case  to  which  the  law  applies.  But  if,  after 
examining  a  very  large  number  of  cases,  we  find  that  the  law 
always  holds  true,  we  are  justified  in  concluding  that  it  is 
true  of  all  cases.  When  we  say  that  all  bodies  attract  one 
another,  do  we  know  this  to  be  absolutely  true?  Certainly 
not.  But  we  do  know  that,  so  far  as  those  bodies  are  con- 
cerned which  come  under  our  observation,  the  statement  is 
true,  and  we  therefore  have  every  reason  to  believe  that  it  is 
true  of  all  bodies. 

Combining  Weights  of  the  Elements. — A  careful  study  of 
the  figures  representing  the  composition  of  chemical  com- 
pounds reveals  a  remarkable  fact  regarding  the  relative 
quantities  of  one  and  the  same  element  which  enter  into 
combination  with  different  elements.  The  proportions  by 
weight  in  which  some  of  the  elements  combine  chemically 
are  stated  in  the  following  table: 


Sulphur,       1; 
Oxygen,        1. 

Iron, 
Oxygen, 

7; 
2. 

Iron, 
Sulphur, 

7; 
4. 

Magnesium,  3; 
Oxygen         2. 

Tin, 
Oxygen, 

59; 
16. 

Zinc, 
Oxygen, 

65; 
16. 

COMBINING  WM&BTS.  25 


Tin, 
Sulphur, 

59; 
16. 

Zinc, 
Sulphur, 

65; 
33. 

Sodium, 
Oxygen, 

23; 

8. 

Sodium, 
Sulphur, 

23; 

16. 

Potassium, 
Oxygen, 

39; 

8. 

Potassium, 
Sulphur, 

39; 
16. 

We  see  that  for  iron,  tin,  zinc,  sodium,  and  potassium 
the  same  figures  are  used,  whether  we  are  dealing  with  the 
compounds  of  these  elements  with  oxygen  or  with  sulphur. 
Now,  if  we  were  to  determine  the  composition  of  all  com- 
pounds which  contain  zinc,  we  should  find  that  the  relative 
quantity  of  zinc  present  could,  in  nearly  all  cases,  be  ex- 
pressed by  the  figure  65.  Similarly,  the  quantity  of  sodi- 
um could  be  expressed  by  the  figure  23,  and  the  quantity 
of  potassium  by  39.  While  in  the  compounds  which  iron 
forms  with  sulphur  and  oxygen  the  relative  quantities  of 
iron  can  be  expressed  by  the  figure  7,  an  examination  of 
other  compounds  containing  iron  would  show  us  that  in 
order  to  express  their  composition  we  should  frequently  be 
obliged  to  use  a  larger  number,  and  56  is  found  to  be  the 
most  convenient  for  the  purpose.  As  with  7  parts  of  iron 
2  parts  of  oxygen  combine;  so  with  56  parts  of  iron  16  parts 
of  oxygen  combine;  and  with  56  parts  of  iron  32  parts  of 
sulphur.  A  study  of  the  compounds  of  oxygen  shows  that 
the  number  best  adapted  to  expressing  the  relative  quantities 
in  which  it  occurs  in  its  compounds  is  16,  and  that  for  sul- 
phur the  most  convenient  number  is  32.  For  every  element 
a  certain  number  can  be  selected,  such  that  the  proportions 
by  weight  in  which  this  element  enters  into  combination 
with  others  can  be  expressed  by  the  number  or  by  a  simple 
multiple  of  it.  These  numbers  express  what  are  called  the 
combining  weights.  It  is  not  by  any  means  an  easy  matter 
to  determine  which  numbers  are  most  convenient  for  all 
cases;  and  if  the  selection  is  to  be  determined  solely  by 


26  INTRODUCTION  T6 

convenience,  there  may  be  differences  of  opinion  as  to 
what  is  most  convenient.  We  shall  see  a  little  later  that, 
while  the  numbers  primarily  express  the  combining  weights 
and  nothing  else,  and  are  based  solely  upon  determinations 
of  the  composition  of  chemical  compounds,  they  have  come 
to  have  a  deeper  significance  and  are  now  determined  by 
methods  which  it  would  be  premature  to  attempt  to  explain 
at  this  stage.  The  facts  which  it  is  of  the  highest  impor- 
tance that  the  student  should  understand  now  are: 

(1)  That  chemical  action  takes  place  between  definite 
masses    of  substances;  and 

(2)  That  the  relative    masses    of  the  elements  which 
enter  into  combination  with  one  another  can  be  expressed 
by  numbers  called  the  combining  weights. 

Law  of  Multiple  Proportion.— The  chief  difficulty  in  the 
way  of  selecting  a  definite  number  for  the  combining 
weight  of  each  element  lies  in  the  fact  that  two  elements 
frequently  combine  in  more  than  one  set  of  proportions. 
Thus,  while  ordinarily  iron  and  sulphur  combine  in  the  pro- 
portion 56  of  iron  to  32  of  sulphur  they  also  combine  in 
the  proportion  56  of  iron  to  64  of  sulphur.  Tin  combines 
with  oxygen  in  two  proportions,  forming  two  distinct  com- 
pounds. In  one  118  parts  of  tin  are  combined  with  16 
parts  of  oxygen;  in  the  other  118  parts  of  tin  are  combined 
with  32  parts  of  oxygen.  The  elements  potassium,  chlorine, 
and  oxygen  combine  in  several  proportions0  In  one  com- 
pound there  are  39  parts  of  potassium,  35.5  parts  of  chlo- 
rine, and  16  parts  of  oxygen;  in  a  second,  39  parts  of  potas- 
sium, 35.5  parts  of  chlorine,  and  32  parts  of  oxygen;  in  a 
third,  39  parts  of  potassium,  35.5  parts  of  chlorine,  and  48 
parts  of  oxygen;  and  in  a  fourth,  39  parts  of  potassium, 
35.5  parts  of  chlorine,  and  64  parts  of  oxygen.  It  will  be 


1$  W  OF  MULTIPLE  PROPORTIONS.  $1 

observed  that  while,  in  these  compounds  the  quantities  of 
oxygen  and  sulphur  united  with  the  same  element  or  ele- 
ments vary,  these  quantities  are  closely  related  to  one  an- 
other. In  the  case  of  iron  and  sulphur  there  is  twice  as 
much  sulphur,  relatively,  in  one  compound  as  in  the  other. 
So,  also,  in  the  compounds  of  tin  and  oxygen,  there  is 
twice  as  much  oxygen  combined  with  a  given  quantity  of 
tin  in  one  case  as  in  the  other.  Finally,  in  the  four  com- 
pounds which  are  made  up  of  potassium,  chlorine,  and  oxy- 
gen, the  quantity  of  oxygen  varies,  being  twice  as  great  in 
the  second  compound  as  in  the  first,  three  times  as  great 
in  the  third,  and  four  times  as  great  in  the  fourth.  These 
facts,  and  others  of  the  same  kind,  are  summed  up  in  the 
Law  of  Multiple  Proportions,  which  may  be  stated  thus: 

If  two  elements,  A  and  B,  combine  in  different  propor- 
tions, the  relative  quantities  of  B  which  combine  with  any 
fixed  quantity  of  A  hear  a  simple  ratio  to  one  another. 

The  significance  of  the  laws  of  definite  and  multiple  pro- 
portions will  scarcely  be  appreciated  at  this  stage;  but,  as 
we  go  on,  we  shall  see  that  they  lie  at  the  foundation  of 
chemistry. 

Chemical  Affinity. — It  is  evident  from  what  we  have  al- 
ready learned  that  there  is  some  power  which  can  hold  sub- 
stances together  in  a  very  intimate  way,  so  intima'te  that 
we  cannot  recognize  them  by  ordinary  means.  "We  do  not 
know  what  causes  the  sulphur  and  iron  to  combine,  but  we 
know  that  they  do  combine.  Similarly,  we  do  not  know 
g  what  causes  a  stone  thrown  in  the  air  to  fall  back  again, 
but  we  know  that  it  falls  back.  It  is  true  that  we  may  say 
that  the  cause  of  the  falling  of  the  stone  is  the  attraction 
of  gravitation,  but  this  does  not  give  us  any  real  informa- 
tion, for  if  we  ask  what  the  attraction  of  gravitation  is, 


TO  CBEMISTUT. 

we  can  only  answer  that  it  is  that  which  causes  all  bodies 
to  attract  each  other.  We  can  also  say,  and  do  say,  that 
the  cause  of  the  chemical  union  of  substances  is  chemical 
affinity.  But  in  so  doing  we  are  only  giving  a  name  to 
something  about  which  we  know  nothing  except  the  effects 
which  it  produces.  All  the  chemical  changes  which  are 
taking  place  around  us  may,  then,  be  referred  to  the  opera- 
tion of  chemical  affinity.  If  this  power  were  suddenly  to 
cease  to  operate,  what  would  be  the  result?  Nature  would 
be  infinitely  less  complex  than  it  now  is.  All  substances 
now  known  to  be  chemical  compounds  would  be  resolved 
into  the  elements  of  which  they  are  composed,  and,  as  far 
as  we  know,  there  would  be  but  about  sixty  or  seventy  dif- 
ferent kinds  of  substances.  All  living  things  would  cease 
to  exist,  and  in  their  place  we  should  have  three  invisible 
gases,  and  something  very  much  like  charcoal.  Mountains 
would  crumble  to  pieces,  and  all  water  would  disappear, 
giving  two  invisible  gases.  The  processes  of  life  in  its 
many  forms  would  be  impossible,  as,  however  subtle  that 
which  we  call  life  may  be,  we  cannot  imagine  it  to  exist 
without  the  existence  of  certain  complex  forms  of  matter; 
and,  as  for  the  life  process  of  larger  animals  and  plants, 
most  complex  chemical  changes  are  constantly  taking  place 
within  them,  and  these  changes  are  absolutely  essential  to 
the  continuation  of  life.  These  considerations  will  suffice 
to  show  the  great  importance  of  the  subject  of  chemistry, 
and  how  impossible  it  is  without  some  knowledge  of  this 
subject  to  form  any  conception  in  regard  to  the  most  im- 
portant phenomena  of  the  universe. 

Summary. — We  have  thus  far  learned  the  difference  be- 
tween physical  and  chemical  change.  We  have  learned  the 
difference  between  elements  and  chemical  compounds,  and 


HOW  TO  STUDY  CHEMISTRY.  29 

between  chemical  compounds  and  mechanical  mixtures.  We 
have  learned  that  there  is  a  close  relation  between  the  differ- 
ent kinds  of  physical  change  and  chemical  change;  and  that 
one  kind  of  change  is  capable  of  producing  other  kinds. 
We  have  learned  how  to  distinguish  chemical  action  from 
other  kinds  of  action,  the  loss  of  their  own  properties 
which  the  substances  suffer  being  a  prominent  character- 
istic of  chemical  action.  And,  finally,  we  have  learned  that 
the  name  chemical  affinity  is  given  to  that  which  causes 
substances  to  act  chemically  upon  one  another,  but  that 
we  do  not  know  what  chemical  affinity  is — we  only  know 
what  effects  it  produces. 

How  to  Study  Chemistry. — We  might  learn  a  great  deal 
about  chemical  facts  and  learn  very  little  in  regard  to  the 
science  of  chemistry.  Science  is  organized  knowledge.  As 
long  as  we  do  not  recognize  any  connection  between  any 
set  of  facts  observed,  or  as  long  as  only  a  few  connections 
are  recognized,  we  cannot  properly  speak  of  a  subject  as  a 
science.  The  subject  must  have  been  studied  for  a  long 
time.  The  laws  governing  the  phenomena  of  the  subject 
must  have  been  discovered  before  that  subject  can  be  re- 
garded as  a  science.  Before  we  can  have  any  conception 
of  the  science  of  chemistry  we  must  become  acquainted 
with  some  of  the  most  important  facts  of  the  science,  and 
we  must  also  learn  what  connection  exists  between  these 
facts.  We  must  become  familiar  with  substances,  as 
they  are,  but  especially  with  the  way  they  act  upon  one 
another.  Unfortunately  for  our  purpose,  but  very  few  sim- 
ple substances  or  elements  occur  in  the  uncombined  form 
in  nature.  While,  therefore,  the  simplest  way  to  begin 
the  study  of  chemical  substances  and  chemical  changes  is 
by  a  consideration  of  the  elements,  the  subject  is  com- 


30  INTRODUCTION  TO  CHEMISTRY. 

plicated  by  the  fact  that  we  cannot  readily  obtain  these 
elements  without  the  aid  of  substances  which  we  have  not 
studied  and  of  processes  which  we  cannot  yet  understand. 
There  are,  however,  two  elements  which  occur  in  nature  in 
enormous  quantities  and  which  can  be  obtained  in  the  un- 
combined  condition  very  easily.  As  the  kinds  of  action 
which  they  exhibit  are  of  great  importance  and  well  calcu- 
lated to  give  an  insight  into  the  nature  of  chemical  action 
in  general,  we  may  profitably  begin  our  study  of  chemical 
phenomena  by  a  consideration  of  these  two  elements. 
They  are  oxygen  and  hydrogen.  In  learning  the  main 
facts  in  regard  to  these  elements  we  shall  learn  a  great 
deal  that  will  be  of  importance  in  enabling  us  to  under- 
stand other  chemical  phenomena ;  we  shall  begin  to  learn 
how  to  study  things  chemically;  and  shall  thus  prepare 
ourselves  for  a  systematic  study  of  the  science  of  chemistry. 
The  Elements  and  their  Symbols. — Before  beginning  this 
study  a  list  of  the  elementary  substances  thus  far  discov- 
ered is  here  given.  The  names  of  those  which  are  most 
widely  distributed,  and  which  form  by  far  the  largest  part 
of  the  earth,  are  printed  in  small  capitals.  The  names  of 
those  which  are  very  rare  are  printed  in  italics.  As  was 
stated  on  page  13,  not  more  than  a  dozen  elements  enter 
largely  into  the  composition  of  the  earth.  These  are  the 
ones  whose  names  are  printed  in  small  capitals.  It  has 
been  calculated  that  the  solid  crust  of  the  earth  is  made  up 
approximately  as  represented  in  the  subjoined  table: 

Oxygen,         44-48. 7#  Calcium,       6.6-0.9£ 

Silicon,          22. 8-36. 2#  Magnesium,  2.7-0.1% 

Aluminium,     9.9-6.1^  Sodium,     •  2.4-2.5^ 

Iron,  9.9-2.4$  Potassium,    1.7-3.1£ 

While  oxygen  forms  a  large  proportion  of  the  solid  crust 
of  the  earth,  it  forms  a  still  larger  proportion  (eight  ninths) 


ELEMENTS  AND  SYMBOLS.  31 

of  water  by  weight,  and  about  one  fifth  of  the  air  by  vol- 
ume. Carbon  is  the  principal  element  entering  into  the 
structure  of  living  things,  while  hydrogen,  oxygen,  and  ni- 
trogen also  are  essential  constituents  of  animals  and  plants. 
Nitrogen  forms  about  four  fifths  of  the  air  by  volume. 

In  representing  the  results  of  chemical  action  it  is  con- 
venient to  use  abbreviations  for  the  names  of  elements  and 
compounds.  Thus,  instead  of  oxygen  we  may  write  simply 
0,  for  hydrogen  H,  for  nitrogen  N,  etc.,  etc.  These  sym- 
bols are  used  in  representing  what  takes  place  when  sub- 
stances act  upon  one  another,  as  will  be  shown  more  clearly 
hereafter.  Very  frequently  the  first  letter  of  the  name  of 
the  element  is  used  as  the  symbol.  If  the  names  of  two 
or  more  elements  begin  with  the  same  letter,  this  letter  is 
used,  but  some  other  letter  of  the  name  is  added.  Thus,  B 
is  the  symbol  of  boron,  Ba  of  Barium,  Bi  of  bismuth,  etc.  In 
some  cases  the  symbol  is  derived  from  the  Latin  names  of  the 
elements.  Thus,  the  symbol  for  iron  is  Fe,  from  Latin 
ferrum;  for  copper,  Cu,  from  cuprum,  for  mercury,  Hg, 
from  hydrargyrum,  etc.  The  symbols  of  the  more  com- 
mon elements  will  soon  become  familiar  by  use.  It  is  not 
desirable  to  attempt  to  commit  them  to  memory  at  this 
stage. 

The  names  themselves  are  derived  from  a  variety  of 
circumstances.  Chlorine  is  derived  from  jAropos-,  which 
means  yellowish  green,  as  this  is  the  color  of  chlorine. 
Bromine  comes  from  /Spco^off,  a  stench,  a  prominent 
characteristic  of  bromine  being  its  bad  odor.  Hydrogen 
comes  from  vdcap,  water,  and  ysreir,  to  produce,  signi- 
fying that  it  is  a  constituent  of  water.  Similarly  nitrogen 
comes  from  rirpor,  nitre,  and  ysveiv,  to  produce,  nitro- 
gen being  one  of  the  constituents  of  nitre.  Potassium  is 
an  element  found  in  potash,  and  sodium  is  found  in  soda. 


INTRODUCTION  TO   CHEMISTRY. 


LIST  OF  THE  ELEMENTS  AND  THEIR  SYMBOLS. 


Antimony      .  . 

....Sb 

Indium  

.      In 

Samarium 

Sm 

Arsenic    ..... 

As 

Iodine  

I 

Scandium  

Sc 

Barium 

.Ba 

Iridium 

.      Ir 

Selenium 

Se 

Bismuth 

Bi 

IRON  

...Fe 

SILICON 

Si 

B 

...La 

Silver     .  .  . 

..As 

Bromine 

Br 

Lead  . 

Pb 

SODIUM 

Na 

Cadmium    .  .  . 

...Cd 

Lithium  

.  ..Li 

Strontium 

Sr 

CcKsium  

....Cs 

MAGNESIUM  .  .  . 

...Mg 

Sulphur  .    ... 

..     .8 

CALCIUM 

.     Ca 

Manganese 

Mn 

Tantalum 

Ta 

CARBON  

c 

Mercury  

.  .  Hg 

Tellurium 

Te 

(Jcrium 

Ce 

Molybcjeuum 

Mo 

1  Jiallium 

Tl 

CHLORINE 

.  Cl 

Niobium    .  .  . 

.    Nb 

Ihorium 

Th 

Chromium  .  .  . 

Cr 

Nickel  

...Ni 

Tin 

Sn 

Cobalt 

Co 

NITROGEN 

N 

Titanium 

Ti 

Columbium 

.  Cb 

Osmium    

.   .Os 

Tungsten 

W 

Conner.  . 

Cu 

OXYGEN  

o 

Uranium 

u 

Didymium  

....Di 

...Pd 

Vanadium 

v 

Erbium  .   .  . 

.  ..   .E 

Phosphorus 

p 

Yttci'bium 

Yt 

Fluorine  ...   . 

F 

Platinum  

...Pt 

Yttrium 

Y 

Gallium 

Ga 

POTASSIUM 

.  K 

Zinc 

Zn 

Glucinum  .... 

Gl 

RJwdium  

.  ..Rh 

Zirconium.  .  .  . 

N.Zr 

Gold.. 

..Au 

.,flb 

^  CHAPTER  II. 

CHEMICAL  PHENOMENA  PRESENTED  BY  OXYGEN. 

IN"  Experiment  3  it  was  shown  that  when  an  electric 
current  is  passed  through  water  two  gases  are  liberated. 
One  of  these  was  distinguished  by  the  readiness  with 
which  substances  burned  in  it.  This  gas  is  oxygen.  A 
gas  with  similar  properties  was  also  obtained  by  heating 
the  red  oxide  of  mercury.  This  is,  in  fact,  the  same  sub- 
stance. 

Occurrence  of  Oxygen. — Oxygen  is  the  most  widely  dis- 
tributed element,  and  it  occurs  also  in  very  large  quantity. 
It  has  been  stated  that  it  forms  between  forty  and  fifty 
per  cent  of  the  solid  crust  of  the  earth,  eight  ninths  of 
water,  and  about  one  fifth  of  the  air. 

Preparation  of  Oxygen. — The  easiest  way  to  make  it  is 
by  heating  some  substance  which  contains  it.  The  sim- 
plest example  of  this  kind  is  that  furnished  by  the  oxide  of 
mercury,  which  when  heated  yields  mercury  and  oxygen. 
If  the  oxide  be  weighed,  and,  after  decomposition,  the 
oxygen  and  the  mercury  be  weighed,  the  weight  of  the 
mercury  plus  the  weight  of  the  oxygen  will  be  found  to  be 
equal  to  the  weight  of  the  oxide.  Therefore  the  oxide 
contains  only  mercury  and  oxygen.  They  are  chemically 
combined,  and  the  heat  overcomes  the  force  which  holds 
them  together.  We  may  represent  the  chemical  compound 
3 


34  INTRODUCTION  TO  CHEMISTRY. 

which  contains  mercury  and  oxygen  by  writing  the  sym- 
bols of  the  two  elements  side  by  side  thus,  HgO,  which 
signifies  primarily  that  the  two  elements  "are  in  chemical 
combination.  If  now  we  wish  to  represent  what  takes 
place  when  the  oxide  is  heated,  we  can  do  so  by  means  of 
an  equation  of  this  kind: 


which  should  be  read,  Mercuric  oxide  gives  mercury  and 
oxygen. 

Another  substance  which  readily  gives  up  oxygen  when 
heated  is  potassium  chlorate.  This  is  a  white  crystallized 
substance,  which  is  manufactured  in  large  quantities.  It 
contains  the  elements  chlorine,  oxygen,  and  potassium. 
When  heated  to  a  sufficiently  high  temperature  it  gives  off 
all  its  oxygen,  a  compound  of  potassium  and  chlorine 
being  left  behind.  The  composition  of  potassium  chlorate 
is  represented  by  the  formula  KC103.  This  formula 
means,  in  the  first  place,  that  the  substance  contains 
potassium,  chlorine,  and  oxygen  in  chemical  combination. 
But  as  definite  weights  of  the  chemical  elements  combine, 
these  symbols  represent  the  definite  weights.  The  symbol 
K  means  not  only  potassium,  but  it  means  39  parts  by 
weight  of  that  element.  The  symbol  Cl  means  35.5  parts 
by  weight  of  chlorine;  and  the  symbol  0  stands  for  16 
parts  by  weight  of  oxygen.  These  figures,  39,  35.5,  and 
16,  are  the  combining  weights  of  the  three  elements  (see 
page  25).  The  figure  3  written  beneath  the  symbol  0 
means  that,  in  the  compound  represented,  the  quantity  of 
oxygen  present  corresponds  to  three  times  its  combining 
weight,  or  instead  of  16  parts  there  are  48  parts  of  oxygen, 
The  symbol  KC10?,  then,  means  that  the  compound 


PREPARATION  OF  OXYGEN.  35 

sented  is  made  up  of  the  three  elements  in  the  proportion 
potassium  39  parts,  chlorine  35.5,  oxygen  48  parts.  If  we 
were  to  analyze  it  we  would  find  that  its  percentage  com- 
position is — 

Potassium 31.84 

Chlorine 28.98 

Oxygen 39.18 

100.00 

This  is  the  invariable  composition  of  the  compound.  If, 
therefore,  we  have  a  certain  weight  of  the  compound,  it  is 
an  easy  matter  to  calculate  how  much  oxygen,  or  chlorine, 
or  potassium  it  contains.  Let  it  be  required,  for  example, 
to  calculate  how  much  oxygen  is  contained  in  4  grams  of 
potassium  chlorate.  We  know  from  the  above  that  39.18 
per  cent  of  potassium  chlorate  is  oxygen,  and  as  39.18 
per  cent  of  4  is  1.57,  it  follows  that  this  is  the  weight  of 
oxygen  in  the  4  grams.  Or  we  may  make  the  calculation 
thus:  As  potassium  chlorate  is  made  up  of  39  parts  of  potas- 
sium, combined  with  35.5  parts  of  chlorine  and  48  parts  of 
oxygen,  in  39  -j-  35.5  -f-  48  =  122.5  parts  of  potassium  chlo- 
rate we  have  48  parts  of  oxygen.  If  in  122.5  parts  there 
are  48  parts,  how  much  is  there  in  4  grams?  Plainly  the 
answer  is  given  by  the  solution  of  the  simple  proportion 

122.5:48  ::  4  :  a?, 

in  which  x  represents  the  actual  quantity  of  oxygen  con- 
tained in  4  grams  of  potassium  chlorate.  Similarly  the 
proportion 

122.5  :39  ::  4:z 

will  give  the  quantity  of  potassium,  and 
123.5:35.5  ::  4: 3? 


36 


INTRODUCTION  TO  CHEMISTRY. 


will  give  the  quantity  of  chlorine  contained  in  4  grams  of 
potassium  chlorate. 

Let  us  now  return  to  the  preparation  of  oxygen.  It  has 
been  found  that  when  potassium  chlorate  is  heated  it  gives 
off  a  gas,  and  this  gas  has  been  proved  to  be  oxygen.  This 
is  in  reality  the  most  convenient  method  for  making 
oxygen. 

EXPEKIMENT  16. — Arrange  an  apparatus  as  shown  in  Fig. 
7.  A  represents  a  flask  of  100  ccm.  capacity.  By  means 


FIG.  7. 


of  a  good-fitting  rubber  stopper  one  end  of  the  bent  glass 
tube  B  is  connected  with  it,  and  the  other  end,  which  should 
turn  upward  slightly,  is  placed  under  the  surface  of 
the  water  in  C.  In  A  put  4  to  5  grams  (about  an  eighth 
of  an  ounce)  potassium  chlorate,  and  gently  heat  by 
means  of  the  lamp.  Notice  carefully  what  takes  place. 
At  first  the  potassium  chlorate  will  melt,  forming  a 
clear  liquid.  If  the  heat  be  increased,  the  liquid  will  ap- 


P&tiPARATION  OP 


pear  to  boil,  and  it  will  soon  be  seen  that  a  gas  is  being 
given  off.  Now  bring  the  inverted  cylinder  D  filled  with 
water  over  the  end  of  the  tube,  and  let  the  bubbles  of  gas 
rise  in  the  cylinder.  After  a  considerable  quantity  of  gas 
has  been  collected  in  this  way  the  action  stops,  the  mass  in 
the  flask  becomes  solid,  and  apparently  the  end  of  the  pro- 
cess is  reached.  But  if  the  heat  be  raised  still  higher, 
gas  will  again  come  off,  and  in  this  second  stage  a  larger 
quantity  will  be  collected  than  in  the  first.  Finally,  how- 
ever, the  end  is  reached,  and  the  substance  left  in  the  flask 
remains  unchanged,  no  matter  how  long  heat  may  be  ap- 
plied. An  examination  of  the  gas  collected  will  show  that 
a  piece  of  wood  will  burn  in  it  very  readily. 

Now  let  us  inquire  exactly  what  has  taken  place  in  the 
experiment  we  have  just  performed.  We  started  with  a 
substance  which  contained  the  elements  potassium,  chlo- 
rine, and  oxygen  held  together  in  chemical  combination  in 
certain  definite  proportions.  We  heated  this,  and  thus 
effected  the  decomposition  of  the  substance,  the  oxygen 
contained  in  it  being  set  free.  If  we  could  examine  the 
substance  left  behind  in  the  flask,  we  should  find  that 
it  contains  no  oxygen,  but  only  potassium  and  chlorine 
in  the  proportions  represented  by  the  symbol  KC1,  i.e., 
as  we  have  seen,  39  parts  of  potassium  to  35.5  parts  of 
chlorine.  For  the  chemist  it  is  not  a  difficult  operation  to 
determine  exactly  what  weight  of  this  substance  is  left  be- 
hind when  a  given  weight  of  potassium  chlorate  is  decom- 
posed by  heat,  and  exactly  how  much  oxygen  is  given  off 
in  the  decomposition.  These  determinations  have  been 
made  over  and  over  again,  and  the  invariable  result  has 
been  that,  for  every  122.5  parts  of  potassium  chlorate  de- 
composed, 39  +  35.5  =  74.5  parts  of  the  compound  KC1, 


TO 

which  is  known  as  potassium  chloride,  are  obtained,  and  48 
parts  of  oxygen  given  off.  These  are  facts:  there  is  no 
speculation  involved  in  the  statement.  Now  the  facts  can 
be  conveniently  represented  by  a  chemical  equation  similar 
to  that  used  to  represent  the  decomposition  of  the  oxide  of 
mercury.  The  facts  are  that  we  start  with  122.5  parts  of 
potassium  chlorate,  KC103,  and  get  74.5  parts  of  potas- 
sium chloride,  KC1,  and  48  parts  of  oxygen.  This  is  all 
represented  by  the  equation: 

KC108        =     KOI      +      30. 
39  +  35.5+48     39  +  35.5  +  3  X  16 

~L2&5  745  ^~48 

The  figure  3  before  the  symbol  of  oxygen  signifies  that 
three  times  the  combining  weight  of  oxygen  is  represented. 
When  the  oxygen  is  in  combination,  as  it  is  in  potassium 
chlorate,  the  3  is  written  below  the  line,  as  already  ex- 
plained. 

If,  then,  we  know  the  combining  weights  of  the  ele- 
ments, this  equation  conveys  to  our  minds  the  idea  of  the 
decomposition  of  potassium  chlorate  into  potassium  chlo- 
ride and  oxygen  by  heat,  and  it  also  conveys  to  our  minds 
the  relations  between  the  quantities  of  the  substances  rep- 
resented. It  is  more  convenient  to  use  such  a  condensed 
expression  than  to  state  in  words  the  jcacts  which  it  repre- 
sents, and  hence  constant  use  is  made  of  similar  expres- 
sions. It  must  be  distinctly  borne  in  mind  that  chemical 
equations  are  fundamentally  different  from  mathematical 
equations.  In  mathematics  if  we  have  a  very  few  simple 
ideas  to  start  with  we  can  construct  a  large  number  oi 
equations  which  must  be  true  if  the  ideas  we  start  with  are 
correct  Mathematical  equations  can  be  worked  out  in  the 


(JSEMIGAL  EQUATIONS.  39 

head.  Chemical  equations,  on  the  other  hand,  simply  rep- 
resent facts  which  have  been  established  by  work  in  the 
laboratory.  The  quantities  and  nature  of  the  substances 
must  have  been  determined  by  some  one,  and  the  equation 
must  be  in  accordance  with  what  has  actually  been  found. 
In  the  experiment  we  noticed  a  fact  which  is  not  taken 
account  of  in  the  equation.  We  noticed  that  the  gas  was 
given  off  in  two  stages :  First,  a  part  came  off  at  a  com- 
paratively low  temperature,  and  then  a  large  quantity 
came  off  at  a  higher  temperature.  If  we  had  measured  the 
gas  given  off  during  the  first  stage,  we  would  have  found 
that  it  was  only  one  third  of  the  total  obtained  by  complete 
decomposition.  If,  further,  we  had  examined  the  solid 
substance  left  behind  in  the  flask,  we  should  have  found 
that  it  consisted  of  two  substances,  one  of  which  was  po- 
tassium chloride,  KC1,  and  the  other  a  compound  which 
contains  more  oxygen  than  the  chlorate.  The  latter  is 
called  potassium  perchlorate,  and  is  represented  by  the 
formula  KC104.  The  relative  quantities  of  the  two  sub- 
stances would  also  be  found  to  correspond  to  the  weights 
represented  by  the  formulas  KC1  and  KC104,  i.e.,  there 
would  be  found  39  -f  35.5  =  74.5  parts  of  potassium  chlo- 
ride to  39  +  35.5  -f  4  X  16  =  138.5  parts  of  potassium  per- 
chlorate. To  represent  these  facts  we  use  the  equation: 

2  KC103  =  KC1  +  KC104  +  20. 

The  figure  2  placed  before  the  symboHor  potassium  chlo- 
rate, KC103,  signifies  that  twice  the  combining  weight  of 
the  compound  takes  part  in  the  change,  i.e.,  twice  the 
sum  of  the  combining  weights  of  the  elements  which  enter 
into  its  composition.  The  quantitative  relations  repre- 
sented are  therefore: 


40  INTRODUCTION  TO  CHEMISTRY. 

2KC103        =     KC1     +        KC104        +    20 
2(39  +  35.5  +  48)     39  +  35.5     39  +  35.5  +  64    2x16 

~~245  74.5~  138J5~  32 

In  the  second  stage  of  the  decomposition  all  the  rest  of  the 
oxygen  is  given  off,  or,  in  other  words,  the  potassium  per- 
chlorate  is  now  decomposed.  The  quantities  of  oxygen 
and  potassium  chloride  obtained  are  represented  by  the 
equation: 

KC104  =  KC1  +  4O. 

Another  good  method  of  preparing  oxygen  consists  in 
heating  black  oxide  of  manganese.  This  is  a  black  sub- 
stance found  in  nature,  called  by  mineralogists  pyrolusite, 
and  by  chemists  manganese  dioxide.  It  consists  of  the  ele- 
ments manganese  and  oxygen  in  the  proportions  repre- 
sented by  the  symbol  Mn02,  the  combining  weight  of 
manganese  being  55.  When  this  compound  is  heated  it 
loses  part  of  its  oxygen,  and  there  is  left  behind  another 
compound  of  manganese  and  oxygen  represented  by  the 
formula  Mn304.  The  action  is  represented  thus: 

3Mn03  =  Mn304  +  20. 

[PROBLEM. — How  much  oxygen  can  be  obtained  by  heating  12 
grams  of  manganese  dioxide?  How  much  manganese  dioxide 
must  be  heated  in  order  to  get  3  grams  of  oxygen?  In  each  case 
how  much  of  the  compound  Mn3O4  would  be  obtained?] 

EXPERIMENT  17. — Make  some  oxygen  by  heating  to  red- 
ness 10  to  15  grams  (about  half  an  ounce)  of  manganese 
dioxide  in  an  iron  ttrfoe  closed  at  one  end  and  connected 
at  the  other  end  by  means  of  a  cork  with  a  bent  glass 
tube. 

The  most  convenient  way  to  make  oxygen  in  the  labor- 
atory is  to  heat  a  mixture  of  equal  parts  of  potassium  chlo- 


P&EPARATIOfr  OF 


41 


rate  and  manganese  dioxide.  This  mixture  gives  off  oxygen 
very  readily  with  the  aid  of  gentle  heat.  The  potassium 
chlorate  is  alone  decomposed  under  these  circumstances, 
the  manganese  dioxide  remaining  unchanged  ;  the  part 
which  it  plays  is  not  understood. 
EXPERIMENT  18.— Mix  25  to  30  grams  (or  about  an 


FIG  .  8. 

ounce)  of  potassium  chlorate  with  an  equ^  weight  of  manga- 
nese dioxide  in  a  mortar.  The  substances  need  not  be  in 
the  form  of  powder.  Heat  the  mixture  in  a  glass  retort, 
and  collect  the  gas  by  displacement  of  water  in  appropriate 
vessels, — cylinders,  bell  glasses,  bottles  with  wide  mouths, 
etc.  It  will  also  be  well  to  collect  some  in  a  gasometer, 


42  INTRODUCTION  TO  CHEMISTRY. 

such  as  are  commonly  found  in  chemical  laboratories,  the 
essential  features  of  which  are  represented  in  Fig.  8.  It  is 
made  either  of  metal  or  of  glass.  The  opening  at  d  can  be 
closed  by  means  of  a  screw  cap.  In  order  to  fill  it  with  water 
open  the  stop-cocks  and  pour  the  water  into  the  upper  part 
of  the  vessel  after  having  screwed  the  cap  on  to  d.  When 
it  is  full,  water  will  flow  out  of  the  small  tube  e.  Now  close 
all  the  stop-cocks,  and  take  the  cap  from  d.  The  water 
will  stay  in  the  vessel  for  the  same  reason  that  it  will  stay 


FIG.  9. 


in  the  cylinder  inverted  with  its  mouth  below  water.  To 
fill  the  gasometer  with  gas,  put  it  over  a  tub  or  sink  and 
introduce  the  tube  from  which  gas  is  issuing  into  the  open- 
ing at  d.  The  gaMill  rise  and  displace  the  water,  which 
will  flow  out  at  d.  When  full,  put  the  cap  on.  We  have 
now  a  supply  of  gas  which  we  can  draw  upon  as  we  may 
need  it.  To  get  the  gas  out  of  the  gasometer,  attach  a 
rubber  tube  to  e,  pour  water  into  the  upper  part  of  the 
gasometer,  open  the  stop-cock  a  and  that  at  e,  when  the 


PHYSICAL  pROPmTim  OF  oxYam.        43 


gag  will  flow  out,  and  the  current  can  be  regulated  by 
means  of  the  stop-  cock  at  e. 

The  arrangement  of  the  retort  is  shown  in  Fig.  9. 

Physical  Properties  of  Oxygen.  —  Having  thus  learned 
how  to  get  oxygen,  we  may  proceed  to  study  its  properties. 
In  the  first  place,  the  gas  is  invisible.  The  slight  cloud 
which  appears  in  the  vessels  when  the  gas  is  first  collected 
is  due  to  the  presence  of  a  very  small  quantity  of  a  sub- 
stance which  is  not  oxygen.  If  the  vessels  are  allowed  to 
stand  for  a  few  minutes  the  cloud  will  disappear,  and  the 
vessels  will  look  the  same  as  if  they  were  filled  with  air. 
The  gas  is  tasteless  and  inodorous. 

EXPEKIMENT  19.  —  Inhale  a  little  of  the  gas  from  one  of 
the  small  bottles. 

Oxygen  is  slightly  heavier  than  the  air.  This  can  be  de- 
termined by  weighing  a  globe  filled  with  air,  then  driving 
out  the  air  by  passing  a  current  of  oxygen  through  it  for 
some  time,  and  weighing  it  again.  If  these  weighings  are 
carefully  made,  it  will  be  found  that  the  relation  between 
the  weights  of  equal  volumes  of  air  and  oxygen  is  1  :  1.1056. 
Or,  in  other  words,  if  a  certain  volume  of  air  weighs  1 
gram,  the  same  volume  of  oxygen  will  weigh  1.1056  gram. 
When  oxygen  is  subjected  to  very  strong  pressure  and  a 
very  low  temperature,  it  becomes  liquid. 

The  properties  of  oxygen  to  which  reference  has  thus  far 
made  are  its  physical  properties.  These  are  its  appearance, 
taste,  smell,  relative  weight,  and  changes  in  its  condition, 
which  still  leave  it  in  the  elementary  form  uncombined 
chemically.  Our  knowledge  of  oxygen  must,  of  course, 
include  a  knowledge  of  its  physical  properties,  but,  from 
the  chemical  standpoint,  it  is  more  important  for  us  to 
know  how  oxygen  acts  chemically.  What  chemical  changes 


44  Itf^ItOfrUCTlON  TO 


is  it  capable  of  bringing  about?  What  conditions  are  nec- 
essary in  order  that  it  may  act  chemically?  What  laws 
govern  the  action?  What  products  are  formed? 

Chemical  Conduct  of  Oxygen.  —  In  order  to  get  an  idea  of 
the  way  in  which  oxygen  acts  upon  some  simple  substances 
under  ordinary  circumstances,  we  may  perform  a  few  experi- 
ments. 

EXPERIMENT  20.  —  Turn  three  of  the  bottles  containing 
oxygen  with  the  mouth  upward,  leaving  them  covered  with 
glass  plates.  Into  one  introduce  some  sulphur  in  a  so-called 
deflagrating-spoon,  which  is  a  small  cup  of  iron  or  brass  at- 
tached to  a  stout  wire  which  passes  through  a  round  metal 
plate,  usually  of  tin.  (See  Fig.  10.)  In  another  put  a  lit- 
tle charcoal  (carbon),  and  in  a  third  a  piece  of  phosphor- 
us* about  the  size  of  a  pea.  Let  them  stand  quietly  and 
notice  what  changes,  if  any,  take  place,  Sulphur,  car- 
bon, and  phosphorus  are  elements,  and  oxygen  is  an 
element.  It  will  be  noticed  that  the  sulphur  and  the 
carbon  remain  unchanged,  while  some  change  is  tak- 
ing place  in  the  vessel  containing  the  phosphorus,  as  is 
shown  by  the  appearance  of  white  fumes.  After  some 
time  the  phosphorus  will  disappear  entirely,  the  fumes  will 
also  disappear,  and  there  will  be  nothing  to  show  us  what 
has  become  of  the  phosphorus.  If  the  temperature  of  the 
room  is  rather  high,  it  may  happen  that  the  phosphorus 
takes  fire.  If  it  should,  it  will  burn  with  an  intensely  bright 

*  Phosphorus  should  be  handled  with  great  care.  It  is  always  kept 
under  water,  usually  in  the  form  of  sticks.  If  a  small  piece  is  wanted, 
take  out  a  stick  with  a  pair  of  forceps,  and  put  it  under  water  in  an 
evaporating-dish.  While  it  is  under  the  water,  cut  off  a  piece  of  the 
size  wanted.  Take  this  out  by  means  of  a  pair  of  forceps,  lay  it 
for  a  moment  on  a  piece  of  filter-paper,  which  will  absorb  most  of  the 
water  ;  then  quickly  put  it  in  the  spoon. 


CHEMICAL   CONDUCT  OF  OXYGEN.  45 

light.  After  the  burning  has  stopped,  the  vessel  will  be 
filled  with  white  fumes,  but  these  will  quickly  disappear, 
and  the  vessel  will  apparently  be  empty. 

These  experiments  show  us  that  oxygen  does  not  act  up- 
on sulphur  and  carbon  when  brought  in  contact  with  them, 
and  that  the  action  upon  phosphorus  is  generally  slight. 
We  might  perform  experiments  of  this  kind  with  a  great 
many  substances,  and  we  should  reach  the  conclusion  that  at 
ordinary  temperatures  oxygen  does  not  act  upon  substances. 
If,  however,  the  substances  be  heated  before  they  are  intro- 
duced into  the  oxygen, the  results  will  be  entirely  different. 
Instead  of  conducting  itself  as  an  inactive  element,  oxygen 
will  act  with  great  ease  upon  many  substances.  Things 
such  as  coal,  wood,  etc.,  which  we  know  will  burn  in  the 
air,  burn  in  oxygen  much  more  readily,  and  several  sub- 
stances such  as  iron,  copper,  etc.,  which  will  not  burn  in 
the  air,  burn  in  oxygen  with  ease. 

EXPERIMENT  21. — In  a  deflagrating-spoon  set  fire  to  a 
little  sulphur  and  let  it  burn  in  the  air.  Notice  whether 
it  burns  with  ease  or  with  difficulty.  Notice  the  odor  of 
the  fumes  which  are  given  off.  Now  set  fire  to  another 
small  portion  and  introduce  it  in  a 
spoon  into  one  of  the  vessels  con- 
taining oxygen,  as  shown  in  Fig. 
10  It  will  be  seen  that  the  sul- 
phur burns  much  more  readily  in 
the  oxygen  than  in  the  air.  No- 
tice the  odor  of  the  fumes  given  off. 
Is  it  the  same  as  that  noticed  when 
the  burning  takes  place  in  the  air?  FlGU  ia 

EXPERIMENT  22. — Perform  similar  experiments  with 
charcoal, 


46  INTRODUCTION  TO  CHEMISTRY. 

EXPERIMENT  23. — Burn  a  small  piece  of  phosphorus  in 
the  air  and  in  oxygen.  In  the  latter  case  the  light  emitted 
from  the  burning  phosphorus  is  so  intense  that  it  is  pain- 
ful to  some  eyes  to  look  at  it.  It  is  better  to  be  cautious. 
The  phenomenon  is  an  extremely  brilliant  one.  The  walls 
of  the  vessel  in  which  the  burning  takes  place  become  cov- 
ered with  a  white  substance  which  afterwards  gradually 
disappears. 

What  has  taken  place  in  these  three  experiments?  In 
the  first  place,  the  substances  were  simply  heated  before 
being  introduced  into  the  oxygen.  Nothing  was  added  to 
them  except  heat.  It  is  clear  that  while  oxygen  does  not 
act  upon  these  substances  at  ordinary  temperatures,  it  does 
act  upon  them  at  higher  temperatures.  But  what  does  the 
action  consist  in?  We  can  determine  this  only  by  a  careful 
study  of  the  substances  before  and  after  the  action.  We 
must  know  not  only  what  substances  are  brought  together, 
but  also  what  weight  of  each;  and  we  must  know  what  sub- 
stances are  left  behind,  and  the  exact  weights  of  these.  In 
the  cases  mentioned  it  would  be  a  difficult  matter  for  one 
not  very  thoroughly  trained  in  the  use  of  chemical  methods 
to  make  all  these  determinations  accurately,  and  unless 
they  were  made  accurately  they  would  fail  to  furnish  us 
with  the  desired  explanation.  The  determinations  have 
fortunately  been  made  so  frequently  that  we  cannot  doubt 
what  we  should  find  were  we  to  repeat  them,  and  for  the 
present  we  shall  have  to  content  ourselves  with  accepting 
the  results,  and  we  may  use  them  as  the  basis  of  our  rea- 
soning. Something,  however,  we  may  learn  for  ourselves 
with  but  little  difficulty.  If  in  the  experiment  with  sul- 
phur we  examine  the  spoon  after  the  burning  stops,  we  find 
that  the  sulphur  has  disappeared.  We  also  notice 


CHEMICAL  CONDUCT  OF  OXTGMN.  47 

there  is  present  an  invisible*  substance,  which  has  a  strong, 
disagreeable  odor.  This  substance  is  not  oxygen  and  it  is 
not  sulphur,but  it  is  a  gas  which  is  formed  by  the  burning 
of  sulphur  in  oxygen.  What  has  become  of  the  oxygen? 
That  it  is  no  longer  present  in  its  original  condition  may 
be  proved  by  introducing  a  burning  stick  into  the  vessel. 
Instead  of  continuing  to  burn  with  increased  activity,  as 
we  have  seen  it  do  in  oxygen,  it  is  extinguished. 

In  the  experiment  with  carbon  the  results  are  similar, 
only  the  invisible  substance  has  no 
odor. 

In  the  experiment  with  phosphor- 
us the  white  substance  which  is  de- 
posited on  the  walls  of  the  vessel 
is  not  phosphorus,  as  is  clear  from 
the  fact  that  it  dissolves  in  water. 
That  the  oxygen  is  used  up  when 
phosphorus  acts  on  it  may  be  shown 
by  the  following  experiment: 

EXPERIMENT  24.  —  Fill  a  tube 
say  30  to  40  cm.  (12  to  15  inches) 
long,  and  2%  to  3  cm.  (1  to  1J 
inches)  wide,  with  oxygen,  and  ar- 
range it  in  a  vessel  over  water,  as 
shown  in  Fig.  11.  Now  fasten  a 
small  stick  of  phosphorus  to  the  end 
of  a  wire  and  push  it  into  the  tube 
so  that  about  J  to  J  inch  of  the  FIO.II. 

phosphorus  is  above  the  water  and  exposed  to  the  oxygen. 
At  first  no  action  will  take  place,  but  after  a  time  white' 

*  The  fumes  first  noticed  subside  if  a  little  water  js  in  tbe  bottle, 


48  INTRODUCTION  TO  CHEMISTRY. 

fumes  will  be  seen  to  rise  from  the  phosphorus,  and  the 
phosphorus  will  begin  to  melt.  This  action  will  be  accom- 
panied by  a  diminution  of  the  volume  of  the  oxygen,  as  will 
be  shown  by  the  rise  of  the  water.  When  the  water  has 
risen  so  as  to  cover  the  phosphorus,  shove  the  stick  up  so 
that  it  is  again  just  above  the  surface  of  the  water.  Some 
of  the  oxygen  will  again  be  used  up.  By  working  carefully, 
and  repeating  this  process  as  many  times  as  may  be  neces- 
sary, the  oxygen  can  all  be  used  up  without  the  active  burn- 
ing of  the  phosphorus.  Usually,  however,  before  the  action 
is  completed,  the  temperature  of  the  phosphorus  becomes 
so  high  that  it  takes  fire,  when  there  is  a  flash  of  light  in 
the  tube  and  a  sudden  rise  of  the  water,  showing  that  the 
gas  is  suddenly  used  up. 

The  chemical  action,  while  the  oxygen  disappears  slowly, 
can  be  shown  to  be  essentially  the  same  in  character  as 
that  which  takes  place  when  the  phosphorus  burns  with 
bright  light. 

These  observations  show  that  when  substances  burn  in 
oxygen  they  disappear,  the  oxygen  also  disappears  and 
something  else  is  formed.  Careful  weighing  has  shown 
that  when  sulphur  burns  every  32  parts  of  sulphur  use  32 
parts  of  oxygen,  and  there  are  formed  64  parts  of  a  com- 
pound containing  both  elements.  The  action  is  repre- 
sented thus: 

S  +  20  =  SO, 
32  +  2  X  16  =  32  +  2  X  16. 

The  compound  represented  by  the  formula  S02,  and 
known  as  sulphur  dioxide,  is  the  invisible  substance  which 
has  the  bad  odor  noticed.  This  is  the  only  thing  formed 
in  the  action, 


CHEMICAL   CONDUCT  OF  OXYGEN.  49 

In  the  case  of  carbon  it  has  been  shown  that  for  every  12 
parts  of  carbon  burned  32  parts  of  oxygen  disappear,  and 
there  are  formed  44  parts  of  a  compound  containing  both 
elements  and  represented  by  the  formula  C03.  The  equa- 
tion representing  the  action  is: 

C  +      20      =          C0a 
12  +  2  X  16  =  12  +  2  X  16. 

The  compound  C0a  is  known  as  carbon  dioxide.  It  is 
the  invisible  substance  left  behind  in  the  vessel  in  which 
carbon  burned  in  oxygen.  It  is  the  only  thing  found 
there,  be'sides  some  carbon  or  oxygen  which  may  have  been 
present  in  excess  of  the  quantities  required  for  the  action. 
In  the  case  of  phosphorus,  for  every  62  parts  of  this  ele- 
ment which  disappear,  80  parts  of  oxygen  are  used  up,  and 
142  parts  of  the  compound  P205  are  formed,  as  represented 
in  the  equation: 

2P  +      50      =  P,06 

2X31  +  5X16  =  2X31  +  5X16 

The  compound  P205  is  known  as  phosphorus  pentoxide. 
It  is  the  white  substance  found  in  the  vessel. 

In  all  three  cases,  then,  the  substances  burned  disappear, 
and  at  the  same  time  a  definite  quantity  of  oxygen  disap- 
pears and  we  get  new  substances  which  are  compounds  of  the 
substances  burned  with  oxygen.  Further,  the  weight  of  the 
substance  burned  plus  the  weight  of  the  oxygen  used  up  is 
exactly  equal  to  the  weight  of  the  substance  formed.  The 
oxygen,  then,  simply  combines  with  the  sulphur,  the  carbon, 
and  the  phosphorus.  The  union  does  not  take  place  unless 
the  temperature  of  the  substances  be  raised  somewhat  before 
they  are  introduced  into  the  oxygen.  The  act  of  combina- 


50  INTRODUCTION  TO  CHEMISTRY. 

tion  is  accompanied  by  an  evolution  of  light  and  heat. 
These,  however,  are  secondary.  They  result  from  the 
rapid  coming-together  of  the  particles  of  the  two  elements, 
caused  by  chemical  attraction,  just  as  a  bullet  is  heated  by 
being  rapidly  projected  against  a  hard  target  which  stops  it. 

We  might  perform  a  great  many  experiments  similar  to 
those  already  studied,  but  a  few  more  will  suffice. 

EXPERIMENT  25.— Straighten  a  steel  watch-spring*  and 
fasten  it  in  a  piece  of  metal,  such  as  is  used  for  fixing  a 
deflagrating-spoon  in  an  upright  position ;  wind  a  little 
thread  around  the  lower  end,  and  dip  it  in  melted  sul- 
phur. Set  fire  to  this  and  insert  it  into  a  vessel  containing 
oxygen.  For  a  moment  the  sulphur  will  burn  as  in  Experi- 
ment 21',  but  soon  the  steel  begins  to  burn  brilliantly,  and 
the  burning  continues  as  long  as  there  is  oxygen  left  in 
the  vessel.  Notice  that  in  this  case  there  is  no  flame,  but 
instead  very  hot  particles  are  given  off  from  the  burning 
iron.  The  phenomenon  is  of  great  beauty,  especially  if  ob- 
served in  a  dark  room.  The  walls  of  the  vessel  become 
covered  with  a  dark  reddish-brown  substance,  some  of  which 
will  also  be  found  at  the  bottom  in  larger  pieces.  This  sub- 
stance is  a  compound  of  iron  and  oxygen  known  as  mag- 
netic oxide  of  iron,  and  represented  by  the  formula  Fe304. 
The  action  is  represented  by  the  equation  : 

3  Fe    +  40    =    Fe304 
3jX  56  +  4  X  16  =  3  X  56  +  4  X  16 

168  64  168  04 

The  reason  why  no  flame  is  observed  in  the  burning  of 
iron  is  that  the  substance  formed  is  a  solid  and  not  a  gas. 

*  Old  watch-springs  can  generally  be  had  of  anv  watch  maker  or 
mender  for  the  asking. 


COMBUSTION.  51 

\Vhafc  we  call  a  flame  is  either  a  gas  burning  or  any  sub- 
stance burning  and  forming  a  gaseous  product.  When 
sulphur  burns  it  forms  a  gaseous  product,  and  is  itself  con- 
verted into  gas  before  it  burns.  It  burns  with  a  flame. 
When  carbon  burns  the  product  is  a  gas.  It  burns  with  a 
slight  flame. 

Burning  in  the  Air.— We  cannot  well  help  noticing  a 
strong  resemblance  between  the  burning  of  substances  in 
oxygen  and  in  the  air,  and  the  question  naturally  suggests 
itself,  Are  these  two  acts  the  same?  Or  is  there  a  difference 
between  them?  To  answer  these  questions,  we  must  burn  the 
siime  things  in  pure  oxygen  and  in  air,  and  see  whether  the 
same  product  is  formed  in  each  case,  and  at  the  same  time 
whether  anything  else  is  formed  ?  If  we  should  make  this 
comparison  in  any  case  we  should  find  that  whether  a  sub- 
stance burns  in  the  air  or  in  pure  oxygen  the  same  product 
is  formed,  and  nothing  else.  It  is  therefore  certain  that 
the  act  of  burning  in  the  air  is  due  to  the  presence  of 
oxygen.  We  shall  learn  later  that  the  reason  why  sub- 
stances do  not  burn  as  readily  in  the  air  as  in  pure  oxygen 
is  that  in  the  air  there  is  present  a  large  quantity  of  another 
gas  which  does  not  act  upon  the  substances  at  all. 

Combustion. — By  the  term  combustion  in  its  broadest 
sense  is  meant  any  chemical  act  which  is  accompanied  by 
an  evolution  of  light  and  heat.  Ordinarily,  however,  it  is 
restricted  to  the  union  of  substances  with  oxygen  as  this 
union  takes  place  in  the  air,  with  evolution  of  light  and  he.it. 
Substances  which  have  the  power  to  unite  with  oxygc>n 
are  said  to  be  combustible,  and  substances  which  have  not 
this  power  are  said  to  be  incombustible.  Most  elements  com- 
bine with  oxygen  under  proper  conditions,  and  are  therefore 
combustible.  Most  compounds  formed  by  the  union  of 


52  INTRODUCTION  TO  CHEMISTRY. 

oxygen  with  combustible  substances  are  incombustible.  For 
example,  the  sulphur  dioxide,  carbon  dioxide,  and  phos- 
phorus pentoxide  obtained  in  Experiments  21,  22,  and  23 
are  incombustible.  They  contain  oxygen,  and  they  cannot 
directly  combine  with  any  more. 

Kindling  Temperature. — We  have  seen  that  substances 
do  not  usually  combine  with  oxygen  at  ordinary  tempera- 
tures, but  that  in  order  to  effect  the  union  the  temperature 
must  be  raised.  If  this  were  not  the  case,  it  is  plain  that 
every  combustible  substance  in  nature  would  burn  up,  for 
the  air  supplies  a  sufficient  quantity  of  oxygen  for  this  pur- 
pose. Some  substances  need  to  be  heated  to  a  high  tem- 
perature before  they  will  combine  with  oxygen;  others  re- 
quire but  very  slight  elevation.  If  we  were  to  subject  a 
piece  of  phosporus,  of  sulphur,  and  of  carbon  to  the  same 
gradual  rise  in  temperature,  we  would  find  that  the  phos- 
phorus takes  fire  very  easily,  only  a  slight  elevation  of  tem- 
perature being  necessary;  next  in  order  would  come  the  sul- 
phur, and  last  the  carbon.  If  we  were  to  repeat  these  ex- 
periments a  number  of  times,  we  should  find  that  the  phos- 
phorus would  always  take  fire  at  the  same  temperature,  and 
a  similar  result  would  be  reached  in  the  cases  of  sulphur 
and  carbon.  Every  combustible  substance  has  its  kindling 
temperature;  that  is,  the  temperature  at  which  it  will  unite 
with  oxygen.  Below  this  temperature  it  will  not  unite  with 
oxygen.  If  a  piece  of  wood  could  be  heated  to  its  kindling 
temperature  all  at  once,  it  would  burn  up  as  r;ipidly  as  it 
could  secure  the  necessary  oxygen;  but  the  burning  does 
not  usually  take  place  rapidly,  for  the  reason  that  only  a 
small  part  of  it  is  at  any  one  time  heated  to  the  kindling 
temperature.  Watch  a  stick  of  wood  burning,  and  watch 
how,  as  we  say,  "  the  fire  creeps"  slowly  along  it.  The  reason 


SLOW  OXIDATION.  53 

of  the  slow  advance  is  simply  this:  only  those  parts  of 
the  stick  which  are  nearest  the  burning  part  become  heated 
to  the  kindling  temperature.  They  take  fire  and  heat  the 
parts  nearest  them,  and  so  on  gradually  throughout  the 
length  of  the  stick. 

Slow  Oxidation. — Substances  may  combine  slowly  with 
oxygen  without  evolution  of  light.  Thus,  if  a  piece  of 
iron  be  allowed  to  lie  in  moist  air,  it  becomes  covered  with 
rust.  This  rust  is  similar  to  the  substance  formed  when  iron 
is  burned  in  oxygen.  Both  are  formed  by  the  union  of  iron 
and  oxygen.  Magnesium  burns  in  the  air,  as  we  have  seen, 
and  forms  a  white  compound  containing  oxygen.  It  burns 
with  increased  brilliancy  in  oxygen,  forming  the  same  com- 
pound. If  left  in  moist  air  for  some  days  or  weeks,  it  be- 
comes covered  with  a  layer  of  the  same  white  substance.  If 
this  be  scraped  oil  and  the  magnesium  again  allowed  to  lie, 
it  will  again  become  covered  with  a  layer  of  the  compound 
with  oxygen,  and  this  may  be  continued  until  the  magnesium 
has  been  completely  converted  into  the  same  substance  that 
is  formed  when  it  burns  in  oxygen  or  in  the  air.  Many 
other  similar  cases  of  slow  oxidation  might  be  described, 
some  of  which,  such  as  the  decay  of  wood,  are  constantly 
taking  place  in  nature.  The  most  important  illustration 
of  slow  oxidation  is  that  which  takes  place  in  our  bodies, 
for,  as  we  shall  see,  the  food  which  we  partake  of  under- 
goes a  great  many  changes;  some  of  the  substances  uniting 
with  oxygen,  and  thus  keeping  up  the  temperature  of  our 
bodies.  This,  however,  is  done  without  evolution  of  light 
and  without  apparent  evolution  of  heat. 

We  take  large  quantities  of  oxygen  into  our  lungs  in 
breathing.  This  acts  upon  various  substances  presented  to 
it,  oxidizing  them  to  other  forms  which  can  easily  be  got 


54  INTRODUCTION  TO  CHEMISTRY. 

rid  of.  More  will  be  said  in  regard  to  the  breathing  proc- 
ess of  animals  and  plants  when  the  subject  of  carbon  and 
its  compounds  with  oxygen  is  considered. 

Heat  of  Combustion. — What  is  the  chief  difference  be- 
tween combustion,  as  we  ordinarily  understand  it,  and 
slow  oxidation?  So  far  as  we  can  judge  by  a  cursory  ex- 
amination, it  is  that  in  the  former  there  is  an  evolution  of 
light  and  heat,  and  in  the  latter  there  is  not.  Eemember- 
ing  that  the  reason  why  a  body  gives  light  is  that  it  is 
heated  to  a  sufficiently  high  temperature,  the  problem  re- 
solves itself  into  a  question  of  heat.  What  difference,  if 
any,  is  there  between  the  quantity  of  heat  given  off  when 
a  substance  burns  and  when  it  undergoes  slow  oxidation 
without  evolution  of  light?  The  answer  is  of  the  highest 
importance.  There  is  no  difference  whatever .  In  one  case 
the  heat  is  all  given  off  in  a  short  space  of  time,  and  there- 
fore the  temperature  of  the  substance  becomes  high  and  it 
emits  light.  In  the  other  the  heat  is  given  off  slowly  and 
continues  for  a  much  longer  time,  and  therefore  the  tem- 
perature of  the  substance  does  not  get  very  high,  as  sur- 
rounding substances  conduct  off  the  heat  as  rapidly  as  it  is 
evolved.  If,  however,  we  were  to  measure  the  quantity  of 
the  heat,  we  would  find  it  to  be  the  same  in  both  cases. 

We  may  measure  the  quantity  of  heat  given  off  in  a 
chemical  reaction  by  allowing  the  reaction  to  fake  place  in 
a  vessel  called  a  calorimeter,  so  constructed  as  to  prevent 
loss  of  heat,  and  containing  a  known  weight  of  water.  The 
temperature  of  the  water  is  noted  at  the  beginning  of  the 
operation  and  at  the  end.  A  quantity  of  heat  is  generally 
stated  by  giving  the  number  of  grams  of  water  which  it 
will  raise  one  degree  Centigrade  in  temperature.  The 
quantity  of  heat  necessary  to  raise  a  gram  of  water  one  de- 


HEAT  OF  DECOMPOSITION.  55 

gree  (Centigrade)  in  temperature  is  the  unit  used  in  heat 
measurement.  It  is  called  the  calorie.  If,  therefore,  we 
say  the  quantity  of  heat  evolved  in  any  reaction  is  250 
calories  (written  generally  250  cal.),  we  mean  simply  a 
quantity  of  heat  which  would  raise  the  temperature  of  250 
grams  of  water  one  degree  (Centigrade)  in  temperature. 

To  repeat,  then: -by  the  heat  of  combustion  of  a  sub- 
stance we  mean  simply  the  quantity  of  heat  given  off  when 
a  certain  weight  of  the  substance  combines  with  oxygen. 
In  order  to  avoid  confusion  it  is  necessary  to  have  an 
agreement  in  regard  to  the  weight  of  substance  which  shall 
be  used  as  the  standard.  This  may  be  a  gram  or  any 
other  weight,  but  for  the  purposes  of  chemistry  it  is  most 
convenient  to  take  weights  in  proportion  to  the  combining 
weights.  Thus,  by  the  heat  of  combustion  of  carbon  is 
meant  the  quantity  of  heat  evolved  by  the  combination  of 
12  grams  of  carbon  with  2  X  16  =  32  grams  of  oxygen. 
By  the  heat  of  combustion  of  sulphur  is  meant  the  quan- 
tity of  heat  evolved  in  the  combination  of  32  grams  of 
sulphur  with  2  X  16  =  32  grams  of  oxygen,  etc. 

It  will  be  found  that  not  only  is  the  heat  of  combustion 
a  fixed  quantity  whether  the  union  with  oxygen  takes 
place  slowly  or  rapidly,  but  that  the  heat  evolved  in  any 
given  chemical  reaction  is  always  the  same,  and  that 
chemical  combination  is  always  accompanied  by  an  evolu- 
tion of  heat, 

Heat  of  Decomposition. — Just  as  it  is  true  that  a  definite 
quantity  of  heat  is  evolved  when  two  or  more  elements 
combine  chemically,  so  also  it  is  true  that  in  order  to  over- 
come the  force  which  holds  these  elements  together  the 
same  quantity  of  heat  is  absorbed.  Thus  the  heat  of  for- 
mation of  the  oxide  of  mercury  is  30,660  cal.;  or,  in  other 


56  INTRODUCTION  TO  CHEMISTRY. 

words,  when  200  grams  of  metallic  mercury  and  16  grams  of 
oxygen  combine,  30,660  calories  are  evolved.  Now,  we  have 
seen  that  when  heat  is  applied  to  the  compound  it  is  de- 
composed into  its  elements.  To  effect  this  decomposi- 
tion, as  much  heat  is  absorbed  as  was  evolved  in  the 
formation. 

Chemical  Energy  and  Chemical  Work. — Any  substance 
which  has  the  power  to  unite  with  others  can  do  chemical 
work,  it  possesses  chemical  energy.  Thus,  all  combustible 
substances  can  do  work.  In  uniting  with  oxygen  heat  is 
evolved,  and  this  can  be  transformed  into  motion.  To  go 
back  to  the  example  of  the  steam-engine,  which  was  re- 
ferred to  in  an  early  part  of  the  book,  the  cause  of  the  mo- 
tion is  the  burning  of  the  fuel.  We  thus  see  that  the 
source  of  the  power  in  the  steam-engine  is  chemical  energy. 
Substances  which  have  not  the  power  to  combine  with 
others  have  no  power  to  do  chemical  work,  or  they  have  no 
chemical  energy.  As  far  as  power  to  combine  with  oxygen 
is  concerned,  water  is  a  substance  of  this  kind,  as  is  also 
carbon  dioxide,  the  gas  formed  when  carbon  is  burned  in 
oxygen.  In  order  that  they  may  do  work,  they  must  first 
be  decomposed  and  their  constituents  put  together  in  some 
form  in  which  they  have  the  power  of  combination.  This 
decomposition  of  carbon  dioxide  and  water  is  taking  place 
constantly  on  the  earth.  All  plant-life  is  dependent  on 
it.  The  products  of  the  action,  i.e.,  the  different  kinds 
of  wood,  have  energy, — they  can  do  chemical  work.  This 
power  to  do  work  has  been  acquired  from  the  heat  of  the 
sun,  to  which  the  decomposition  of  the  carbon  dioxide 
and  water  is  mainly  due.  We  have  thus  a  transformation 
of  the  sun's  heat  into  chemical  energy,  which  is  stored  up 
in  the  combustible  woods.  The  quantity  of  heat  which 


OXIDES-THEIR  NAMES.  57 

would  be  given  off  in  burning  the  wood  would  be  exactly 
equal  to  the  quantity  used  up  in  its  formation. 

Oxides. — The  compounds  of  oxygen  with  other  elements 
are  called  oxides.  To  distinguish  between  different  oxides 
the  name  of  the  element  with  which  the  oxygen  is  in  com- 
bination is  prefixed.  Thus  the  compound  of  zinc  and 
oxygen  is  called  zinc  oxide  ;  that  of  calcium  and  oxygen, 
calcium  oxide  ;  that  of  silver  and  oxygen,  silver  oxide,  etc. 
When  an  element  forms  more  than  one  compound  with 
oxygen,  suffixes  are  made  use  of  to  distinguish  between 
them.  Thus  in  the  case  of  copper  there  are  two  oxides 
which  have  the  formulas  Cu20  and  CuO.  The  former  is 
known  as  cuprous  oxide  and  the  latter  as  cupric  oxide. 
That  oxide  which  contains  the  smaller  proportion  of  oxy- 
gen in  combination  with  any  fixed  quantity  of  the  other 
element  is  designated  by  the  suffix  ous,  that  which  contains 
the  larger  proportion  of  oxygen  is  designated  by  the  suffix  ic. 
In  other  cases  the  number  of  combining  weights  of  oxygen 
contained  in  the  compound  is  indicated  by  the  name. 
Thus  manganese  dioxide  is  MnOa;  sulphur  trioxide  is  SOS, 
etc. 


CHAPTER  III. 
HYDROGEN. 

IN  Experiment  3  it  was  found  that  when  an  electric  cu  r- 
rent  is  passed  through  water  two  gases  are  obtained,  one  of 
which  we  have  since  studied  and  found  to  be  oxygen.  The 
other,  it  will  be  remembered,  takes  fire  and  burns,  and  is 
thus  easily  distinguished  from  oxygen.  This  second  gas  is 
hydrogen,  which  we  may  now  proceed  to  study. 

Occurrence. — Hydrogen  is  found  in  nature  very  widely 
distributed,  and  in  large  quantity.  It  forms  one-ninth  the 
weight  of  water,  and  is  contained  in  all  substances  which 
enter  into  the  composition  of  plants  and  animals. 

Preparation  of  Hydrogen. — It  may  be  prepared: 

(a)  By  decomposition  of  water  by  means  of  the  electric 
current ; 

(b)  By  decomposition  of  water  by  the  action  of  certair 
metals ; 

(c)  By  the  action  of  substances  known  as  acids  on  metals. 
The  following  experiments  will  illustrate  these  methods: 
EXPERIMENT  26. — Repeat  Experiment  3  and  examine  the 

gusos. 

EXPERIMENT  27. — Throw  a  small  piece  of  sodium*  on 

*  The  metals  sodium  and  potassium  are  kept  under  oil.  When  a 
small  piece  is  wanted  take  out  one  of  the  larger  pieces  from  the  bottle, 
roughly  wipe  off  the'£il  with  filter  paper  and  cut  off  a  piece  the 
size  needed.  It  is  not  advisable  to  use  a  piece  larger  than  a  pea. 


PREPARATION  OF  HYDROGEN.  69 

water.  While  it  is  floating  on  the  surface  apply  a  lighted 
match  to  it.  A  yellow  flame  will  appear.  This  is  burning 
hydrogen,  the  flame  being  colored  yellow  by  the  presence  of 
the  sodium,  some  of  which  also  burns.  Make  the  same  ex- 
periment with  potassium.  The  flame  appears  in  this  case 
without  the  aid  of  the  match.  It  has  a  violet  color  which 
is  due  to  the  burning  of  some  of  the  potassium.  The  gas 
given  off  in  these  experiments  is  either  burned  at  once  or  es- 
capes into  the  air.  In  the  case  of  the  potassium  the  action 
takes  place  rapidly,  and  the  heat  evolved  is  sufficient  to  set 
fire  to  the  gas.  In  the  case  of  the  sodium  the  heat  evolved 
does  not  set  fire  to  the  gas.  In  order  to  collect  it  unburned, 
it  is  only  necessary  to  allow  the  decomposition  to  take  place, 
so  that  the  gas  will  rise  in  an  inverted  vessel  filled  with  water. 
For  this  purpose  fill  a  good-sized  test-tube  with  water  and 
invert  it  in  a  vessel  of  water.  Cut  off  a  piece  of  sodium 
not  larger  than  a  pea,  wrap  it  in  a  layer  or  two  of  filter 
paper,  and  with  the  fingers  or  a  pair  of  curved  forceps  bring 
it  quickly  below  the  mouth  of  the  test-tube  and  let  go  of  it. 
It  will  rise  to  the  top,  the  decomposition  of  the  water  will 
take  place  quietly,  and  the  gas  formed,  being  unable  to  es- 
cape, will  remain  in  the  tube.  By  repeating  this  operation 
in  the  same  tube  a  second  portion  of  gas  maybe  made,  and 
so  on  until  enough  has  been  made. 

Examine  the  gas  and  see  whether  it  acts  like  the  hydro- 
gen obtained  from  water  by  means  of  the  electric  current. 
What  evidence  have  you  that  they  are  the  same?  Is  this 
evidence  sufficient  to  prove  the  identity  of  the  two? 

The  metals  sodium  and  potassium  disappear  in  these  ex- 
periments, and  we  get  hydrogen.  What  becomes  of  the 
metals?  and  what  is  the  source  of  the  hydrogen?  If  after 
the  action  has  stopped  the  water  be  examined,  it  will  be 


60  INTRODUCTION  TO  CHEMISTRY. 

found  to  contain  something  in  solution.  It  now  has  a  pe- 
culiar taste  which  we  call  alkaline;  it  feels  slightly  soapy  to 
the  touch;  it  changes  certain  vegetable  colors.  If  the  water 
is  evaporated  off,  a  white  substance  remains  behind  which  is 
plainly  neither  sodium  nor  potassium.  In  solid  form  or  in 
very  concentrated  solution  it  acts  very  strongly  on  animal  and 
vegetable  substances,  disintegrating  many  of  them.  On  ac- 
count of  this  action  it  is  known  as  caustic  soda,  or,  in  the 
case  of  potassium,  as  caustic  potassa.  Analysis  has  shown 
that  they  are  made  up  as  represented  by  the  formulas 
NaOH  and  KOH.  From  any  given  quantity  of  water  de- 
composed, only  half  the  hydrogen  is  given  off.  The  action 
is  represented  by  the  equations: 


As  will  be  shown,  the  composition  of  water  is  represented 
by  the  formula  H20.  The  hydrogen  and  oxygen  are  held 
together  by  chemical  affinity,  as  we  say.  Now,  if  anything 
is  brought  in  contact  with  the  water  which  has  a  stronger 
affinity  for  oxygen  than  hydrogen  has,  the  water  will  be 
decomposed,  and  the  hydrogen  will  give  way  to  the  new 
substance.  This  is  what  takes  place  in  the  case  of  sodium 
and  potassium.  These  metals  have  a  stronger  affinity  for 
oxygen  than  hydrogen  has,  and  therefore  they  displace  a 
part  of  the  hydrogen  when  a  compound  is  formed  which  is 
so  stable  that  it  is  not  decomposed  by  the  metals. 

Chemical  Action  Caused  by  Differences  between  the  Attrac- 
tions of  the  Elements  for  One  Another.  —  We  have  seen  that 
chemical  action  can  be  effected  by  means  of  heat  and  elec- 
tricity; and  also  that  when  certain  elements  are  brought  to- 
gether the  attraction  which  they  have  for  one  another  causes 


PREPARATION  OF  HYDROGEN. 


61 


them  to  combine  directly,  as  in  the  case  of  phosphorus  and 
oxygen.  By  far  thj  largest  number  of  chemical  reactions, 
however,  which  we  have  to  deal  with  are  the  result  of 
bringing  together  two  or  more  chemical  compounds,  the 
constituents  of  which  rearrange  themselves  in  the  form  of 
new  compounds  in  accordance  with  the  strength  of  the  at- 
tractions of  the  constituents.  Thus,  if  we  have  two  com- 
pounds one  of  which  is  made  up  of  the  elements  A  and  B 
and  another  made  up  of  C  and  D,  and  the  attraction  of  A 
for  C  is  greater  than  that  of  A  for  B  or  0  for  D,  and,  at 
the  same  time,  B  and  D  have  an  attraction  for  each  other, 
then,  on  bringing  together  the  compounds  A  B  and  C  D  a 
reaction  will  take  place  thus : 

AB  +  C  D  =  AC+BD. 

There  are  various  conditions  which  may  modify  this  law, 
but  these  will  be  readily  understood  by  the  aid  of  examples 
which  will  soon  present  themselves. 

EXPERIMENT  28. — Certain  metals  which  do  not  decompose 


water  at  ordinary  temperatures,  or  which  decompose  it  slowly, 
decompose  it  easily  at  elevated  temperatures.  This  is  true  of 
iron.  If  steam  be  passed  through  a  tube  containing  pieces 
of  iron  heated  to  redness,  decomposition  of  the  water  takes 


62  INTRODUCTION  TO  CHEMISTRY. 

place,  the  oxygen  is  retained  by  the  iron,  which  enters  in  to 
combination  with  it,  while  the  hydrogen  is  liberated.  In 
this  experiment  a  porcelain  tube  with  an  internal  diameter 
of  from  20  to  25  mm.  (about  an  inch)  and  a  gas  furnace 
are  desirable,  though  a  hard  glass  tube  and  a  charcoal  fur- 
nace will  answer.  The  arrangement  of  the  apparatus  is 
shown  in  Fig.  12. 

The  hydrogen  may  be  collected  by  displacement  of  water, 
as  in  the  case  of  oxygen.  The  reaction  which  takes  place 
is  represented  thus  : 

3Fe  +  4H20  =  Fe304  +  8H. 

PROBLEMS. — How  much  water  could  be  decomposed  by  20  kilo- 
grams (or  40  pounds)  of  iron?  and  how  much  would  the  hydro- 
gen obtained  weigh?  one  litre  of  hydrogen  at  0°  C.  and  under  the 
normal  atmospheric  pressure  of  760  mm.  weighs  0.089578  gram. 
What  will  be  the  volume  of  hydrogen  obtained  by  using  up  20 
kilograms  of  iron  in  the  decomposition  of  water? 

Many  other  substances  have  the  power  to  decompose 
water  and  set  hydrogen  free.  The  fact  that  a  combustible 
gas  can  be  obtained  from  water  has  led  to  many  attempts 
to  manufacture  gas  for  heating  and  illuminating  purposes 
from  water.  There  is,  however,  no  cheap  substance  known 
to  us  which  has  the  power  to  decompose  water  at  ordinary 
temperatures.  All  other  methods  must  involve  the  use  of 
heat,  and  it  is  not  unfrequently  the  case  that  the  quantity 
of  heat  required  to  effect  the  decomposition  is  greater  than 
that  which  would  be  obtained  by  burning  the  hydrogen 
formed.  In  the  manufacture  of  the  so-called  "  water  gas" 
which  is  now  extensively  used  in  the  United  States  both  for 
illuminating  and  heating  purposes,  water  is  decomposed 
by  means  of  carbon  which  is  used  in  the  form  of  hard  coal. 
The  reaction  takes  place  mainly  according  to  this  equation: 


THE  COMMON  ACIDS.  (53 

Both  products  are  gases,  and  both  burn;  and  when  this 
mixture  is  enriched  by  some  of  the  oils  obtained  from 
petroleum,  it  burns  well  and  gives  a  good  light. 

By  far  the  most  convenient  method  for  making  hydrogen 
consists  in  treating  a  metal  with  an  acid.  As  will  be  seen 
later,  acids  are  substances  which  contain  hydrogen,  and 
which  are  characterized  by  the  fact  that  they  give  up  this 
hydrogen  very  easily  and  take  up  other  elements  in  the 
place  of  it.  Among  the  common  acids  found  in  every  lab- 
oratory are  hydrochloric  acid,  sulphuric  acid,  and  nitric  acid. 
The  chemistry  of  these  compounds  will  be  considered  indue 
time;  but  as  we  shall  be  obliged  to  use  them  before  they  are 
studied  systematically,  a  few  words  in  regard  to  them  are 
desirable  at  this  time. 

Hydrochloric  acid  is  a  compound  of  hydrogen  and  chlo- 
rine. It  is  a  gas  which  dissolves  easily  in  water.  It  is  this 
solution  which  we  use  in  the  laboratory,  and  which  is 
manufactured  in  enormous  quantities  in  connection  with  the 
manufacture  of  soda  or  sodium  carbonate.  Its  chemical 
formula  is  HC1.  It  is  frequently  called  "  Muriatic  acid." 

Sulphuric  acid  is  a  compound  of  sulphur,  oxygen,  and 
hydrogen  in  the  proportions  represented  by  the  formula 
H2S04.  It  is  an  oily  liquid  and  is  frequently  called  "  Oil 
of  Vitriol."  It  is  manufactured  in  very  large  quantities,  as 
it  plays  an  important  part  in  many  of  the  most  important 
chemical  industries. 

Nitric  acid  is  a  compound  containing  nitrogen,  oxygen, 
and  hydrogen  In  the  proportions  represented  in  the  formula 
HN03.  It  is  a  colorless  liquid,  though  as  we  get  it  it  is 
commonly  colored  somewhat  yellow. 

When  a  metal,  as  zinc,  is  brought  in  contact  with  hydro- 
chloric or  sulphuric  acid,  an  evolution  of  gas  takes  place  at 
once. 


64 


INTRODUCTION  TO  CHEMISTRY. 


EXPERIMENT  29. — In  a  cylinder  or  test-tube  put  some 
small  pieces  of  zinc,  and  pour  upon  it  some  ordinary  hydro- 
chloric acid.  After  the  action  has  continued  for  a  minute 
or  two  apply  a  lighted  match  to  the  mouth  of  the  vessel 
The  gas  will  take  fire  and  burn.  If  sulphuric  acid  diluted 
with  five  or  six  times  its  volume  of  water*  be  used  in- 


Fio.  13. 


FIG.  14. 


stead  of  hydrochloric  acid,  the  same  result  will  be  reached. 
The  gas  evolved  is  hydrogen.  For  the  purpose  of  collecting 
the  gas  the  operation  is  best  performed  in  a  bottle  with  two 
necks  called  a  Wolff's  flask  (see  Fig.  13),  or  in  a  wide- 
mouthed  bottle  in  which  is  fitted  a  cork  with  two  holes 
(see  Fig.  14).  Through  one  of  the  holes  passes  a  funnel- 

*If  it  is  desired  to  dilute  ordinary  concentrated  sulphuric  acid  with 
water,  the  acid  should  be  poured  slowly  into  the  water  while  the 
mixture  is  constantly  stirred.  If  the  water  is  poured  into  the  acid, 
the  heat  evolved  at  the  places  where  the  two  come  in  contact  may  be 
so  great  as  to  convert  the  water  into  steam  and  cause  the  strong  acid 
to  spatter. 


PREPARATION  OF  HYDROGEN.  65 

tube,  and  through  the  other  a  glass  tube  bent  in  a  convenient 
form. 

The  zinc  used  is  usually  what  is  known  as  granulated 
zinc.  It  is  prepared  by  melting  it  in  a  ladle  and  pouring 
the  molten  metal  from  an  elevation  of  four  or  five  feet  into 
water.  The  advantage  of  this  form  is  that  it  presents  a 
large  surface  to  the  action  of  the  acids.  A  handful  of  this 
zinc  is  introduced  into  the  bottle,  and  enough  of  a  cooled 
mixture  of  sulphuric  acid  and  water  (1  volume  concen- 
trated acid  to  6  volumes  water)  poured  upon  it  to  cover 
it.  Usually  a  brisk  evolution  of  gas  takes  place  at  once. 
Wait  for  two  or  three  minutes,  and  then  collect  some  of  the 
gas  by  displacement  of  water.  When  the  action  becomes 
slow,  add  more  of  the  dilute  acid.  It  will  be  well  to  fill 
several  cylinders  and  bottles  with  the  gas,  and  also  a  ga- 
someter, from  which  it  can  .be  taken  as  it  is  needed  for 
experiments. 

The  action  which  takes  place  in  the  case  of  zinc  and 
hydrochloric  acid  is  represented  thus  : 


The  compound  Zn01a  is  called  zinc  chloride.  It  is  left 
in  solution  in  the  vessel.  If  there  is  sufficient  zinc  present, 
all  the  hydrochloric  acid  will  be  changed  in  accordance  with 
the  above  equation. 

In  the  case  of  sulphuric  acid  and  zinc  the  action  is  rep- 
resented thus  : 

Zn  +  H2S04  =  ZnS04  +  2H. 

The  compound  ZnS04  is  called  zinc  sulphate.  It  is  the 
substance  commonly  known  as  white  vitriol.  It  is  in  solu- 
tion in  the  flask,  and  can  be  obtained  by  evaporating  off 

the  water. 
5 


66  INTRODUCTION  TO  CHEMISTRY. 

EXPERIMENT  30. — After  the  action  is  over  pour  the  con- 
tents of  the  flask  through  a  filter  into  an  evaporating-dish, 
and  boil  off  the  greater  part  of  the  water,  so  that,  on  cooling, 
the  substance  contained  in  solution  will  be  deposited.  If 
the  operation  is  carried  on  properly,  the  substance  will  be 
deposited  in  regular  forms  called  crystals.  It  is  zinc  sul- 
phate, ZnS04,  formed  by  the  replacement  of  the  hydrogen 
of  the  sulphuric  acid  by  zinc. 

PROBLEMS. — How  much  zinc  would  it  take  to  give  200  litres  of 
hydrogen?  How  much  zinc  sulphate  would  be  formed?  How 
much  hydrogen  would  be  formed  by  the  action  of  50  grams  of 
zinc  on  sulphuric  acid?  How  much  sulphuric  acid  would  be  used 
up?  The  combining  weight  of  zinc  is  65. 

Physical  Properties  of  Hydrogen. — Hydrogen  is  a  color- 
less, inodorous,  tasteless  gas.  Made  by  the  action  of  zinc 
on  acids,  it  has  a  slightly  disagreeable  odor.  This  is  due  to 
the  presence  of  impurities.  If.it  be  passed  through  certain 
substances  which  have  the  power  to  destroy  the  impurities, 
the  odor  is  destroyed. 

EXPERIMENT  31. — Pass  some  of  the  gas  through  a  wash 
cylinder  containing  a  solution  of  potassium  permanganate  ; 
collect  some  of  it,  and  notice  whether  it  has  an  odor  or 
not.  The  apparatus  should  be  arranged  as  shown  in  Fig. 
15.  The  solution  of  potassium  permanganate  is,  of  course, 
contained  in  the  small  cylinder  A,  and  the  tubes  so  arranged 
that  the  gas  bubbles  through  it. 

The  gas  is  not  poisonous,  and  may  therefore  be  inhaled 
with  impunity.  We  could  not,  however,  live  in  an  atmos- 
phere of  hydrogen,  as  we  need  oxygen.  It  is  the  lightest 
known  substance,  being  fourteen  and  a  half  times  lighter 
than  the  air  and  sixteen  times  lighter  than  oxygen.  Its 
lightness  may  be  shown  by  a  number  of  simple  experi- 
ments, 


PROPERTIES  OF  HYDROGEN. 


67 


EXPERIMENT  32. — Place  a  vessel  containing  hydrogen 
with  the  mouth  upward  and  uncovered.  In  a  short  time 
examine  the  gas,  and  see  whether  it  is  hydrogen. 


FIG.  15. 


EXPERIMENT  33. — Gradually  bring  a  vessel  containing 
hydrogen  with  its  mouth  upward  below  an  inverted  vessel 


FIQ.  16. 


containing  air,  in  the  way  shown  in  Fig.  16.     The  air  will 
be  displaced.     On  examination,  the  inverted  vessel  will  be 


68  INTRODUCTION  TO  CHEMISTET. 

found  to  contain  hydrogen,  while  the  one  with  the  mouth 
upward  will  contain  none.  The  gas  is  thus  poured  up- 
wards. 

EXPERIMENT  34. — Soap-bubbles  filled  with  hydrogen 
rise  in  the  air.  This  experiment  may  be  best  performed 
by  connecting  an  ordinary  clay  pipe  by  means  of  a  piece  of 
rubber  tubing  with  the  exit- tube  of  a  gasometer  filled  with 
hydrogen.  Small  balloons  of  collodion  are  also  made  for 
the  purpose  of  showing  the  lightness  of  hydrogen. 

Balloons  are  always  filled  with  hydrogen,  or  some  other 
light  gas.  Some  kinds  of  illuminating  gas  are  rich  in 
hydrogen,  and  may  therefore  be  used  for  the  purpose. 

A  litre  of  hydrogen  at  0°  Centigrade,  and  under  the  pres- 
sure of  760  mm.,  weighs  0.089578  gram.  Its  specific  grav- 
ity is  0.0691.  A  comparison  of  these  figures  with  the  corre- 
sponding figures  for  oxygen  leads  to  an  interesting  observa- 
tion. The  weight  of  a  litre  of  oxygen  is  1.429  grams  ;  its 
specific  gravity  is  1.10563.  The  ratio  of  the  weight  of 
equal  volumes  of  hydrogen  and  oxygen  to  each  other  is 
1 : 16,  or 

0.089578  :  1.429  ::  1  :  16. 

But  the  figures  1  and  16  are  the  combining  weights  of 
these  elements;  that  is  to  say,  they  are  the  figures  best 
adapted  to  expressing  the  relative  quantities  of  these  ele- 
ments which  enter  into  combination.  There  appears, 
therefore,  to  be  a  close  connection  between  the  absolute 
weights  of  equal  volumes  of  these  gases  and  the  figures  rep- 
resenting their  combining  weights.  We  shall  see  that  this 
connection  is  observed  between  the  weights  of  other  gases; 
the  explanation,  however,  had  better  be  postponed  until 
some  other  facts,  the  knowledge  of  which  is  necessary  in 


PROPERTIES  OF  HYDROGEN.  69 

order  to  make  the  explanation  intelligible,  shall  have  been 
considered. 

When  subjected  to  a  very  low  temperature  and  high 
pressure  hydrogen  becomes  liquid. 

Chemical  Properties  of  Hydrogen.— Under  ordinary  cir- 
cumstances, hydrogen  is  not  a  particularly  active  element. 
It  does  not  unite  with  oxygen  at  ordinary  temperatures, 
but,  like  wood  and  most  other  combustible  substances, 
needs  to  be  heated  up  to  the  kindling  temperature  before 
it  will  burn.  We  have  seen  that  it  burns  if  a  lighted  match 
be  applied  to  it.  The  flame  is  colorless,  or  very  slightly 
blue.  As  burned  under  ordinary  circumstances,  the  flame 
is  colored,  in  consequence  of  the  presence  of  foreign  sub- 
stances; but  that  it  is  colorless  when  the  gas  is  burned 
alone  can  be  shown  by  burning  it  from  a  platinum  tube, 
which  is  itself  not  acted  upon  by  the  heat. 

EXPERIMENT  35. — If  there  is  no  small  platinum  tube 
available,  roll  up  a  small  piece  of  platinum  foil  and  melt  it 
into  the  end  of  a  glass  tube,  as  shown  in  Fig.  17.  Con- 
nect the  burner  thus  made  with  the  gasometer  containing 
hydrogen,  and  after  the  gas 
has  been  allowed  to  issue  from 
it  for  a  moment,  set  fire  to  it. 
In  a  short  time  it  will  be  seen 
that  the  flame  is  practically 
colorless,  and  gives  no  light.  FIG.  17. 

That  it  is  hot  can  be  readily  shown  by  holding  a  piece 
of  platinum  wire  or  a  piece  of  some  other  metal  in  it. 

Hydrogen  burns.  We  have  seen  that  this  consists  in 
combining  with  oxygen.  On  the  other  hand,  substances 
which  burn  in  the  air  are  extinguished  when  put  in  a  vessel 
containing  hydrogen.  This  is  equivalent  to  saying  that  a 


70 


INTRODUCTION  TO  CHEMISTRY. 


body  which  is  uniting  with  oxygen  does  not  continue  to 
unite  with  oxygen  when  put  in  an  atmosphere  of  hydro- 
gen, and  does  not  combine  with  the  hydrogen.  This  is  ex- 
pressed by  saying  that  hydrogen  does  not  support  combus- 
tion. The  following  experiment  shows  this. 

EXPERIMENT  36.— Hold  a  cylinder  filled  with  hydrogen 
with  the  mouth  downward.  Insert  into  the  vessel  a  lighted 
taper  held  on  a  bent  wire,  as  shown  in  Fig.  18.  The  gas 
takes  fire  at  the  mouth  of  the  vessel, 
but  the  taper  is  extinguished.  On 
withdrawing  the  taper  and  holding 
the  wick  for  a  moment  in  the  burning 
hydrogen,  it  will  take  fire,  but  on  put- 
ting it  back  in  the  hydrogen  it  will 
again  be  extinguished.  Other  burn- 
ing substances  should  be  tried  in  a 
similar  way. 

As  when  hydrogen  burns  it  corn- 
is,  bines  with  oxygen,  a  product  should 
be  obtained  in  which  both  hydrogen  and  oxygen  are  pres- 
ent. In  the  experiments  performed  we  have  seen  no  evi- 
dence of  the  formation  of  such  a  product,  simply  for  the 
reason  that  when  formed  it  is  an  invisible  gas,  and,  though 
it  can  easily  be  condensed  to  a  liquid,  no  precautions  were 
taken  to  get  it  in  this  form.  The  product  is,  in  fact,  ordi- 
nary water,  which  we  will  next  study. 


CHAPTER  IV. 
COMBINATION  OF  HYDROGEN  AND  OXYGEN.— WATER. 

WATER  was  long  regarded  as  an  element  until,  towards 
the  end  of  last  century,  the  discovery  of  hydrogen  and 
oxygen,  and  of  the  nature  of  combustion,  led  to  the  discov- 
ery of  its  true  composition. 

Occurrence. — The  wide  distribution  of  water  on  the  earth 
is  familiar  to  every  one.  But  water  also  occurs  in  forms 
and  conditions  which  prevent  its  immediate  recognition. 
Thus  all  living  things  contain  a  large  proportion  of  water, 
which  can  be  driven  off  by  heat.  If  a  piece  of  wood  or  a 
piece  of  meat  be  heated,  water  passes  off. 

EXPERIMENT  37. — In  a  dry  tube  heat  gently  a  small 
piece  of  wood.  What  evidence  do  you  obtain  that  water  is 
given  off?  Do  the  same  thing  with  a  piece  of  fresh  meat. 

The  proportion  of  water  in  animal  and  vegetable  sub- 
stances is  very  great.  If  the  body  of  a  man  weighing  150 
pounds  were  to  be  put  in  an  oven  and  thoroughly  dried, 
there  would  be  left  only  about  40  pounds  of  solid  matter, 
all  the  rest  being  water.  As  all  meat,  vegetables,  and  food- 
stuffs in  general  contain  a  similar  large  proportion  of  water, 
it  is  evident  that  water  is  a  very  important  article  of  com- 
merce. When  we  buy  four  pounds  of  beef,  we  pay  for  about 
three  pounds  of  water  and  one  of  solid  matter. 

Water  also  occurs  in  another  form  in  which  it  does  not 


72  INTRODUCTION  TO  CHEMISTRY. 

easily  reveal  its  presence.  This  is  as  water  of  crystalliza- 
tion. 

EXPERIMENT  38.— Take  some  of  the  crystals  of  zinc  sul- 
phate obtained  in  Experiment  31,  Spread  them  out  on  a 
layer  of  filter  paper,  and  finally  press  two  or  three  of  them 
between  folds  of  the  paper.  Examine  them  carefully. 
They  appear  to  be  quite  dry,  and  in  the  ordinary  sense  they 
are  dry.  Put  them  in  a  dry  tube,  and  heat  them  gently, 
when  it  will  be  observed  that  water  condenses  in  the  upper 
part  of  the  tube,  while  the  crystals  lose  their  lustre,  becom- 
ing white  and  opaque,  and  at  last  crumbling  to  powder. 

EXPERIMENT  39. — Perform  a  similar  experiment  with 
some  gypsum,  which  is  the  natural  substance  from  which 
"  Plaster  of  Paris"  is  made. 

EXPERIMENT  40. — Heat  a  few  small  crystals  of  copper 
sulphate  or  blue  vitriol.  In  this  case  the  loss  of  water  is 
accompanied  by  a  loss  of  color.  After  all  the  water  is 
driven  off,  the  powder  left  behind  is  white.  On  dissolving 
it  in  water,  however,  the  solution  will  be  seen  to  be  blue ; 
and  if  the  solution  be  evaporated  until  the  substance  is  de- 
posited, it  will  appear  in  the  form  of  blue  crystals. 

Many  compounds  when  deposited  from  solutions  in  water 
in  the  form  of  crystals  combine  with  definite  quantities  of 
water.  This  water  is  not  present  as  such,  but  is  held  in 
chemical  combination.  Hence  the  substance  does  not  ap- 
pear moist,  though  it  may  contain  more  than  half  its  weight 
of  water.  This  water  of  crystallization  is,  in  some  way 
which  we  do  not  understand,  essential  to  the  form  of  the 
crystal.  If  it  is  driven  off  by  heat,  the  crystal  is  destroyed, 
Some  compounds  combine  under  different  circumstances 
with  different  quantities  of  water,  the  form  of  the  crystals 
yarying  with  the  quantity  of  water  in  combination. 


WATER  OF  CRYSTALLIZATION.  f3 

Compounds  differ  greatly  as  regards  the  ease  with  which 
they  give  up  water  of  crystallization.  In  general,  it  is 
given  off  when  the  compound  containing  it  is  heated  to  the 
temperature  of  boiling  water.  But  some  compounds  give 
it  up  by  simple  contact  with  the  air.  This  is  true  of  so- 
dium sulphate,  or  Glauber's  salt,  which  contains  a  quantity 
of  water  of  crystallization  represented  by  the  formula 
Na2S04.10H20. 

EXPERIMENT  41.— Select  a  few  crystals  of  sodium  sul- 
phate which  have  not  lost  their  lustre.  Put  them  on  a 
watch-glass,  and  let  them  lie  exposed  to  the  air  for  an  hour 
or  two.  They  soon  lose  their  lustre,  and  undergo  the 
changes  noticed  in  heating  zinc  sulphate. 

Compounds  which  lose  their  water  of  crystallization  by 
simple  contact  with  the  air  are  said  to  effloresce.  They  are 
called  efflorescent. 

Some  compounds  if  deprived  of  their  water  of  crystalliza- 
tion will  take  it  up  again  when  allowed  to  lie  in  an  atmos- 
phere containing  moisture.  As  the  air  always  contains 
moisture,  it  is  only  necessary  to  expose  such  compounds  to 
the  air  in  order  to  notice  the  phenomenon.  It  is  well 
shown  by  the  compound  calcium  chloridje,  CaCl2.  This 
substance  has  a  remarkable  power  of  attracting  water  to 
itself  and  holding  it  in  combination. 

EXPERIMENT  42. — Expose  a  few  pieces  of  calcium  chlo- 
ride to  the  air.  Its  surface  will  soon  give  evidence  of  the 
presence  of  moisture,  and,  after  a  time,  the  substance  will 
dissolve  in  the  water  which  is  absorbed. 

Substances  which  absorb  water  from  the  air  are  said  to 
deliquesce.  They  are  called  deliquescent. 

Formation  of  Water  and  Proofs  of  its  Composition.— 
In  order  to  determine  the  composition  of  water,  as  well  as 


74  INTRODUCTION  TO  CHEMI8TKY. 

that  of  any  other  compound,  we  must  analyze  it.  We  may 
simply  determine  what  substances  enter  into  its  composi- 
tion without  determining  the  relative  quantities  of  these 
substances.  In  this  case  we  make  what  is  called  a  quali- 
tative analysis.  If,  however,  we  not  only  determine  what 
substances  are  present,  but  also  in  what  quantities  they 
are  present,  we  then  make  a  quantitative  analysis.  Both 
qualitative  and  quantitative  analyses  are  necessary  to  enable 
us  to  determine  the  composition  of  a  substance. 

The  composition  of  a  substance  may  also  be  determined 
by  putting  together  its  constituents  and  causing  them  to 
combine  chemically.  An  operation  of  this  kind  is  called  a 
synthesis.  A  synthesis,  then,  is  the  opposite  of  an  analy- 
sis. Just  as  we  may  make  a  qualitative  or  a  quantitative 
analysis,  so  also  we  may  make  a  qualitative  or  a  quantita- 
tive synthesis. 

These  processes  are  well  illustrated  in  the  operations 
necessary  to  determine  the  composition  of  water.  That 
water  contains  hydrogen  and  oxygen  has  already  been  shown 
in  Experiment  3.  It  will  now  be  well  to  repeat  the  experi- 
ment and  see  whether  we  can  learn  anything  more  regard- 
ing the  composition  of  water  than  that  it  contains  hydrogen 
and  oxygen.  In  the  first  place,  the  question  suggests  itself, 
In  what  proportions,  by  weight  and  by  volume,  are  the  gases 
combined  ? 

EXPEEIMENT  43. — The  tubes  in  the  apparatus  used  in 
Experiment  3,  or  some  other  similar  apparatus,  should  be 
marked  by  means  of  a  file,  or  by  etching,  so  that  equal  divi- 
sions can  be  recognized.  Tubes  thus  divided  so  that  the 
divisions  indicate  cubic  centimetres  are  most  convenient 
for  the  purpose.  Let  the  gases  formed  by  the  action  of  the 
electric  current,  as  in  Experiment  3,  rise  in  the  graduated 


COMPOSITION  OF  WATER.  75 

tubes,  and  observe  the  volumes.  It  will  be  seen  that  when 
one  tube  is  just  full  of  gas,  the  other,  if  it  be  of  the  same 
size,  will  be  only  half  full.  On  examining  the  gases  the 
larger  volume  will  be  found  to  be  hydrogen,  and  the 
smaller  volume  oxygen. 

No  matter  how  many  times  we  may  make  this  experiment, 
we  shall  always  find  that  for  every  volume  of  oxygen  we 
get  two  volumes  of  hydrogen.  We  already  know  the  rela- 
live  weights  of  equal  volumes  of  the  two  gases,  so  that  we 
can  easily  calculate  the  relative  weights  of  the  gases  ob- 
tained from  water  by  the  action  of  the  electric  current. 
The  ratio  of  the  weights  of  equal  volumes  of  hydrogen  and 
oxygen  is  1  : 16.  Therefore,  if  we  have  two  volumes  of 
hydrogen  combined  with  one  volume  of  oxygen,  the  ratio 
between  the  weights  is  2  : 16  or  1  :  8.  Although  we  know 
from  the  above  experiment  that  hydrogen  and  oxygen  are 
obtained  from  water  in  the  proportion  of  two  volumes  of 
the  former  to  one  of  the  latter,  or  of  one  part  by  weight  of 
the  former  to  eight  parts  by  weight  of  the  latter,  we  do  not 
know  from  the  experiment  that  this  represents  the  actual 
composition  of  water.  For  it  may  be  that  other  elements 
besides  hydrogen  and  oxygen  are  contained  in  the  water, 
and  it  may  be  that  all  the  hydrogen  and  oxygen  are  not  set 
free  by  the  action  of  the  electric  current.  We  might  de- 
termine whether  either  of  these  possibilities  is  true  or  not 
by  decomposing  a  weighed  quantity  of  water,  and  weighing 
the  hydrogen  and  oxygen  obtained  from  it.  If  we  should 
find  that  the  sum  of  the  weights  of  hydrogen  and  oxygen  is 
equal  to  the  weight  of  the  water  decomposed,  this  fact 
would  be  evidence  that  only  hydrogen  and  oxygen  are  con- 
tained in  water,  and  that  they  are  present  in  the  propor- 
tions stated.  The  same  thing  can  be  satisfactorily  proved 


76  INTRODUCTION  TO  CHEMISTRY. 

by  effecting  the  synthesis  of  water.  In  the  first  place,  we 
can  show  that  water  is  formed  when  hydrogen  burns  in  the 
air,  and,  knowing  that  burning  is  combining  with  oxygen, 
we  are  justified  in  concluding  that  water  consists  of  hydro- 
gen and  oxygen. 

EXPERIMENT  44. — Pass  hydrogen  from  a  generating-flask 
or  a  gasometer  through  a  tube  containing  some  substance 
that  will  absorb  moisture,  for  all  gases  made  in  the  or- 
dinary way  and  collected  over  water  are  charged  with 
moisture.  "We  have  seen  in  Experiment  42  that  calcium 
chloride  has  the  power  to  absorb  moisture.  It  is  exten- 
sively used  in  the  laboratory  for  the  purpose  of  drying 
gases,  and  it  may  be  used  in  the  present  experiment.  It 
should  be  in  granulated  form,  not  powdered  After  passing 
the  hydrogen  through  the  calcium  chloride,  pass  it  through 
a  tube  ending  in  a  narrow  opening,  and  set  fire  to  it.  If 
now  a  dry  vessel  be  held  over  the  flame,  drops  of  water  will 
condense  on  its  surface  and  run  down.  A  convenient  ar- 
rangement of  the  apparatus  is  shown  in  Tig.  19. 


FIG.  19. 


A  is  the  calcium  chloride  tube.     Before  lighting  the  jet 
hold  a  glass  plate  in  the  escaping  gas,  and  see  whether 


COMPOSITION  OF  WATER.  77 

water  is  deposited  on  it.  Light  the  jet  before  putting  it 
under  the  bell  jar,  otherwise  if  hydrogen  is  allowed  to 
escape  into  the  vessel  it  will  contain  a  mixture  of  air  and 
hydrogen,  and  this  mixture,  as  we  shall  soon  see,  is  explo- 
sive. 

We  have  thus  effected  the  qualitative  synthesis  of  water; 
how  can  we  effect  the  quantitative  synthesis  ? 

If  we  mix  hydrogen  and  oxygen  together,  and  allow  the 
mixture  to  stand  unmolested,  it  remains  unchanged.  If, 
however,  we  should  bring  a  spark  or  a  flame  in  contact 
with  the  mixture,  a  violent  explosion  would  occur,  and  a 
careful  examination  would  show  that  the  explosion  is  the 
result  of  the  combination  of  the  two  gases.  The  noise  is 
caused  by  the  sudden  great  expansion  of  the  gases  occa- 
sioned by  the  development  of  heat.  This  expansion  is  in- 
stantly followed  by  a  contraction. 

EXPERIMENT  45. — Mix  hydrogen  and  oxygen  in  the  pro- 
portions of  about  2  volumes  of  hydrogen  to  1  volume  of 
oxygen  in  a  gasometer.  Fill  soap-bubbles,  made  as  directed 
in  Experiment  34,  with  this  mixture  and  allow  them  to 
rise  in  the  air.  As  they  rise  bring  a  lighted  taper  in  con- 
tact with  them,  when  a  sharp  explosion  will  occur.  Great 
care  must  be  taken  to  keep  all  flames  away  from  the  vicin- 
ity of  the  gasometer  while  the  mixture  is  in  it.  This  ex- 
periment may  be  conveniently  performed  by  hanging  up, 
about  six  to  eight  feet  above  the  experiment-table,  a  good- 
sized  tin  funnel-shaped  vessel  with  the  mouth  downward. 
Now  place  a  gas  jet  or  a  small  flame  of  any  kind  at  the 
mouth  of  the  vessel.  If  the  soap-bubbles  are  allowed  to 
rise  below  this  apparatus  they  will  come  in  contact  with 
the  flame  and  explode  at  once.* 

*  The  same  apparatus  may  be  used  in  experimenting  with  soap 
bubbles  filled  with  hydrogen. 


78  INTRODUCTION  TO  CHEMISTRY. 

This  experiment  simply  shows  that  a  mixture  of  hydro- 
gen and  oxygen  explodes  when  brought  in  contact  with  a 
flame,  and  that  the  gases  do  not  act  upon  each  other  at 
ordinary  temperatures.  In  order  to  show  that  when  the 
explosion  occurs,  water  is  formed,  and  in  what  proportions 
the  gases  combine,  it  is  necessary  to  work  in  closed  vessels 
which  are  so  constructed  as  to  enable  us  accurately  to  meas- 
ure the  volumes  of  the  gases.  The  experiment  is  so  im- 
portant that,  if  possible,  it  had  better  be  performed,  at  least 
by  the  teacher,  before  the  class.  The  apparatus  necessary 
is  not  expensive,  and  the  manipulation  not  difficult. 
The  vessel  in  which  the  gases  are  brought  together  and 
caused  to  combine  is  called  a  eudiometer  (from  svdiot, 
calm  air,  and  ^srpoy,  a  measure)-.  It  is  simply  a  tube 
graduated  in  millimetres  and  having  two  small  plati- 
num wires  passed  through  it  at  the  closed  end,  nearly 
meeting  inside  and  ending  in  loops  outside,  as  shown 
in  Fig.  20.  The  eudiometer  is  filled  with  mercury,  in- 


FIG.  20. 


verted  in  a  mercury  trough,  and  held  in  upright  position 
by  means  of  proper  clamps.  A  quantity  of  pure  hydrogen 
is  now  passed  up  into  the  tube  and  its  volume  accurately 
measured.  About  half  this  volume  of  oxygen  is  then  intro- 
duced, and  after  the  mixture  has  been  allowed  to  stand  for 
a  few  minutes,  a  spark  is  passed  between  the  wires  in  the 
eudiometer  by  connecting  the  loops  with  the  poles  of  a 
small  Kuhmkorif  coil  or  with  a  Leyden  jar.  Under  these 
circumstances  the  explosion  takes  place  noiselessly  and  with 
very  little  danger.  If  the  interior  of  the  tube  was  dry  be- 


MEASUREMENT  OF  GASES.  79 

fore  the  explosion,  it  will  be  seen  to  be  moist  afterwards, 
and  a  marked  decrease  in  the  volume  of  the  gases  is  also 
observed.  That  water  is  the  product  of  the  action  has 
been  proved  beyond  any  possibility  of  a  doubt,  over  and 
over  again.  As  the  liquid  water  which  is  formed  occupies 
an  almost  inappreciable  volume  as  compared  with  the  vol- 
ume of  the  gases  which  combine,  the  decrease  in  volume 
represents  the  total  volume  of  hydrogen  and  oxygen  which 
have  combined.  Now,  if  the  experiment  be  performed 
with  the  two  gases  in  different  proportions,  it  will  be  found 
that  only  when  they  are  mixed  in  the  proportion  of  two 
volumes  of  hydrogen  and  one  volume  of  oxygen  do  they 
completely  disappear  in  the  explosion.  If  there  is  a  larger 
proportion  of  hydrogen  present,  the  excess  is  left  over.  If 
there  is  a  larger  proportion  of  oxygen  present,  the  excess 
of  oxygen  is  left  over.  We  see,  thus,  that  when  hydrogen 
and  oxygen  combine  to  form  water,  they  do  so  in  the  pro- 
portion of  two  volumes  of  hydrogen  to  one  volume  of  oxy- 
gen. In  order  that  the  student  may  fully  appreciate  this 
experiment,  it  is  desirable  that  he  should  at  this  point 
familiarize  himself  with  the  precautions  necessary  in  meas- 
uring the  volumes  of  gases,  if  he  has  not  already  done  so. 
Measurement  of  the  Volume  of  a  Gas.— The  volume  of  a 
gas  varies  with  the  temperature  and  pressure.  When  the 
temperature  of  a  gas  is  raised  one  degree  Centigrade  its 
volume  is  increased  ^  part.  If,  therefore,  the  volume  of 
a  gas  at  0°  be  T7,  at  t°  its  volume  v  will  be 

.F       or        , 

This  expression  may  also  be  written 
v  =  V+  0.00366  t .  V       or        V  =  F(l  +  0.00366  t). 


80  INTRODUCTION  TO  CHEMISTRY. 

From  this  it  follows  that 

F== !L_ 

1  +  0. 00366  t' 

It  is  customary  to  reduce  the  observed  volume  of  a  gas 
to  the  volume  which  it  would  have  at  0°.  The  correction 
is  made  in  accordance  with  the  above  expression.  Thus, 
if  we  measure  a  volume  of  gas,  and  find  it  to  be  250  cubic 
centimetres  at  15°,  and  wish  to  find  what  its  volume  would 
be  at  0°,  we  proceed  as  follows:  In  this  case  v,  the  observed 
volume,  is  250  cc.;  t,  the  temperature,  is  ]5°.  Substituting 

these  values  in  the  equation  V  =  — -  TTT.  >  we  have 

1  -j-  U.  OOobbt 

250 


F  = 


0.00360.15 


from  which  we  get  236.99  as  the  value  of  V.  But  the  vol- 
ume of  a  gas  varies  also  according  to  the  pressure.  If  the 
pressure  be  doubled,  the  volume  is  decreased  to  one  half ; 
and  if  the  pressure  be  decreased  to  one  half,  the  volume  is 
doubled,  and  so  on.  In  other  words,  the  volume  of  a  gas 
varies  inversely  with  the  pressure.  Increase  the  pressure 
two,  three,  or  four  times  and  the  volume  becomes  one 
half,  one  third,  or  one  fourth,  and  vice  versa.  If  the  gas 
has  the  volume  Fat  the  pressure  P  and  at  pressure  p  the 
volume  v,  these  values  bear  to  each  other  the  relations  ex- 
pressed in  the  equation 

P  V  =  pv. 

The  pressure  is  usually  stated  in  millimetres,  and  refer- 
ence is  to  the  height  of  a  column  of  mercury  which  the 
pressure  corresponds  to.  A  gas  contained  in  an  open  ves- 
sel, or  in  a  vessel  over  mercury  in  water,  in  which  the  level 
of  the  liquid  inside  and  outside  the  vessel  is  the  same,  is 


MEASUREMENT  OF  GASES. 


81 


under  the  pressure  of  the  atmosphere.  What  that  is  we 
learn  from  the  barometer.  As  this  pressure  varies,  it  is 
necessary  to  read  the  barometer  whenever  a  gas  is  meas- 
ured, and  then  to  reduce  the  observed  volume  to  certain 
conditions  which  are  accepted  as  standard.  If  the  gas  is 
measured  in  a  tube. over  mercury  or  water,  and  the  level  of 
the  liquid  inside  the  tube  is  higher  than  that  outside,  the 
gas  is  under  diminished  pressure,  the  amount  of  diminu- 
tion depending  on  the  height  of  the  column  of  mercury  or 
water  in  the  tube.  Thus,  if  the  arrangement  be  as  repre- 
sented in  Fig.  21  and  the  height 
of  the  mercury  column  above  the 
level  of  the  mercury  in  the  trough 
be  100  millimetres,  and  the  pres- 
sure of  the  atmosphere  be  760 
millimetres,  then  the  gas  in  the 
tube  is  not  under  the  full  atmos- 
pheric pressure,  for  the  atmos- 
pheric pressure  exerted  on  the  gas 
is  supporting  a  column  of  mercury 
100  millimetres  high,  and  the  pres- 
sure actually  brought  to  bear  on 
the  gas  corresponds  to  760  —  100  Fig.  21. 

=  660  mm.  Suppose  that  in  this  case  the  volume  of  gas 
actually  measured  is  75  cc.  Call  this  v.  What  would  be 
the  actual  volume  V  of  the  gas  under  the  standard  pres- 
sure 760  mm.  ?  We  have  seen  that 

VP  =  vp. 

Now  P  =  760,  v  =  75,  and  p  =  660.  Therefore,  760  F  = 
75  X  660,  or  V=  -  -  ==  65.13. 

6 


82  INTRODUCTION  TO  CHEMISTRY. 

In  all  cases  it  is  necessary  to  make  a  correction  similar 
to  this  in  dealing  with  the  volumes  of  gases.  The  correc- 
tion for  temperature  and  that  for  pressure  may  be  made  in 
one  operation,  the  formula  being 


-  __  , 
760(1  +  0.003660 

in  which  F  =  the  volume  of  the  gas  at  0°  and  760  mm. 
pressure  ;  v  =  the  observed  volume  ;  t  —  the  observed  tem- 
perature ;  p  =  the  pressure  under  which  the  gas  is  meas- 
ured. 

[PROBLEMS.  —  The  volume  of  a  gas  contained  in  a  eudiometer 
measures  42  cc.  The  height  of  the  mercury  column  over  which  it 
stands  is  68  mm.  The  barometer  indicates  an  atmospheric  pres- 
sure of  746  mm.  The  temperature  is  18°C.  What  would  be  the 
volume  of  the  gas  at  0°  and  760  mm.  pressure  ? 

The  volume  of  a  gas  contained  in  a  vessel  over  a  column  of 
mercury  85  mm.  high  measures  24  cc.  The  barometer  indicates  a 
pressure  of  774  mm.  The  temperature  is  19°.  What  would  be 
the  volume  of  the  gas  under  normal  conditions,  i.e.,  t  =  0°  and 
P  =  760  mm.? 

The  volume  of  a  gas  contained  in  a  vessel  over  a  liquid,  the 
level  of  the  liquid  inside  and  outside  being  the  same  :  v  =  80  cc.  ; 
t  =  20°  ;  p  =  740  mm.  What  is  the  value  of  V  or  the  volume  at 
0°  and  760  mm.?] 

It  will  be  found  hereafter  that  some  of  the  most  impor- 
tant ideas  which  have  been  introduced  into  chemistry 
with  the  view  of  explaining  the  regularities  observed  in  the 
quantities  of  substances  which  act  upon  one  another  chemi- 
cally have  their  origin  in  observations  upon  the  conduct  of 
gases.  It  is  therefore  highly  desirable  that  the  student 
should  fully  understand  what  is  meant  by  the  expression 
"  the  volume  of  a  gas  under  standard  conditions,"  and  it  is 
recommended  that  he  be  given  a  few  actual  examples  in 
which  he  shall  make  all  the  observations  and  calculations 
necessary. 

The  presence  of  water  vapor  in  a  gas  also  influences  its 


COMPOSITION  OF  WATER.  33 

volume,  and  this  must  be  taken  into  account  in  refined 
work.  The  student  is  referred  to  some  larger  book  for 
details. 

Let  us  now  return  to  the  problem  of  determining  the  com- 
position of  water  by  means  of  explosions  in  the  eudiometer. 
It  remains  to  be  shown  how  to  calculate  the  composition  of 
water  from  the  observations  made. 

Calculation  of  the  Results  Obtained  in  Exploding  Mixtures 
of  Hydrogen  and  Oxygen.— Having  determined  that  when- 
ever hydrogen  and  oxygen  combine,  they  do  so  in  the  pro- 
portion 1  volume  oxygen  to  2  volumes  hydrogen,  and  that 
when  they  combine,  the  volume  of  water  formed  measures  so 
little  as  to  amount  to  nothing  in  the  measurements,  we 
know  that  whenever  a  mixture  of  hydrogen  and  oxygen  is 
exploded,  no  matter  in  what  proportions  they  may  be  pres- 
ent, the  volume  of  gas  which  disappears  as  such  consisted  of 
2  volumes  of  hydrogen  and  1  volume  of  oxygen,  or,  in  other 
words,  one  third  of  the  volume  which  disappears  was  oxy- 
gen and  two  thirds  hydrogen.  Take  this  example:  A 
quantity  of  hydrogen  corresponding  to  60  cc.  under  standard 
conditions  is  introduced  into  a  eudiometer;  40  cc.  of  oxygen 
are  added.  What  contraction  will  there  be  on  exploding  the 
mixture?  Plainly  the  60  cc.  of  hydrogen  will  combine  with 
30  cc.  of  oxygen.  The  90  cc.  of  gas  will  disappear,  and  the 
10  cc.  of  oxygen  will  remain  unchanged.  From  a  total 
volume  of  100  cc. ,  therefore,  we  get  a  contraction  to  10  cc. 
One  third  of  the  contraction  represents  the  oxygen  and 
two  thirds  the  hydrogen. 

Synthesis  of  Water  by  Passing  Hydrogen  over  Heated 
Oxides. — The  synthesis  of  water  may  be  effected  by  passing 
hydrogen  over  a  compound  containing  oxygen  and  heated 
to  a  sufficiently  high  temperature.  A  convenient  sub-- 


84  INTRODUCTION  TO  CHEMISTRY. 

stance  for  this  purpose  is  the  compound  of  copper  and 
oxygen  known  as  copper  oxide  or  black  oxide  of  copper. 
It  contains  its  elements  in  the  proportions  represented  in 
the  formula  CuO,  the  combining  weight  of  copper  being 
63.  When  hydrogen  is  passed  over  this  compound  at  or- 
dinary temperatures  no  action  takes  place.  If,  however, 
the  temperature  be  raised  to  low  redness  the  hydrogen 
combines  with  the  oxygen,  forming  water,  and  the  copper 
is  left  behind  as  such.  The  reaction  is  represented  thus: 


EXPERIMENT  46.  —  Arrange  an  apparatus  as  shown  in 
Fig.  22. 

A  is  a  Wolff's  flask  for  generating  hydrogen.  To  re- 
move impurities  the  gas  is  passed  through  a  solution  of 


FIG.  22. 

potassium  permanganate  contained  in  the  wash  cylinder  5. 
The  cylinder  C  contains  concentrated  sulphuric  acid,  and 
the  U-shaped  tube  D  contains  granulated  calcium  chlo- 
ride, both  of  them  serving  to  remove  moisture  from  the 
gas.  The  pure  dry  hydrogen  is  now  passed  through  the 
hard  glass  tube  E,  which  contains  a  layer  of  copper  oxide. 
After  the  apparatus  is  filled  with  hydrogen  the  gas  jet  is 
lighted  and  the  copper  oxide  heated  to  low  redness.  Soon 
moisture  will  be  seen  in  the  end  of  the  tube  and  drops  of 
water  will  collect  in  the  vessel  G-. 
In  this  case  the  loss  in  weight  of  the  copper  oxide  repre- 


COMPOSITION  OF  WATER.  85 

sents  oxygen.  If,  therefore,  we  should  weigh  the  copper 
oxide  before  the  experiment,  and  afterward  the  copper,  and 
should  also  collect  and  weigh  the  water  formed,  we  could 
from  the  figures  obtained  easily  calculate  the  relative 
weight  of  oxygen  contained  in  the  water.  The  water  can 
easily  be  collected  bypassing  it  into  a  tube  filled  with  cal- 
cium chloride.  If  the  tube  is  weighed  before  the  experi- 
ment and  after  it,  the  gain  in  weight  will  represent  the 
weight  of  the  water  collected.  All  these  weighings  can  be 
made  without  difficulty  on  a  chemical  balance  such  as 
is  found  in  every  chemical  laboratory.  Where  time  will 
permit  it  will  be  well  for  each  student  to  go  through  with 
this  experiment.  A  few  experiments  of  this  kind  will 
serve  to  impress  upon  the  mind  the  reality  of  the  quantita- 
tive relations  about  which  he  is  constantly  hearing.  If  it 
is  performed  a  small  hard  glass  tube  from  12  to  15  centi- 
metres (5  to  6  inches)  long  and  about  1  centimetre  (or 
half  an  inch)  internal  diameter  should  be  used  in  place  of 
the  tube  E  in  the  qualitative  experiment  above  described. 
The  tube  is  drawn  out  at  one  end  and  a  small  plug  of  as- 
bestos put  in  the  small  end.  Connection  with  the  weighed 
calcium  chloride  tube  is  made  at  this  end.  The  tube  is 
first  dried  thoroughly  and  weighed.  Then  a  few  grams  of 
coarsely  granulated  copper  oxide  are  introduced  into  it. 
After  the  experiment  the  tube  and  the  copper  are  weighed 
again.  The  calcium  chloride  should  of  course  be  weighed 
before  and  after  the  experiment.  The  results  are  calcu- 
lated thus: 

Let          x  =  weight  of  tube  +  copper  oxide  before  the 

experiment; 

y  =  weight  of  tube  -f  copper  after  the  experi- 
ment. 


86  INTRODUCTION  TO  CHEMISTRY. 

Then  x—y  =  weight  of  oxygen   taken  from  the  copper 

oxide. 

Let  a  =  weight  of  calcium   chloride  tube  before  ; 

£=         "        "         "         "         "         after; 
Then  I—a  —  weight  of  water  formed. 
If  the  experiment  is  carefully  performed,  it  will  be  found 

sy*  _,__,  nt 

that  the  ratio  7 — -  is  very  nearly  f . 

Oxidation  and  Reduction. — Any  substance  which  like 
hydrogen  has  the  power  to  abstract  oxygen  from  com- 
pounds containing  it  is  called  a  reducing  agent.  The  proc- 


FIG.  23. 


ess  of  abstracting  oxygen  from  a  compound  is  called 
reduction.  Reduction  and  oxidation  are  therefore  com- 
plementary processes.  We  shall  hereafter  become  ac- 
quainted with  a  number  of  important  and  interesting 
reducing  processes. 

Applications  of  the  Heat  Evolved  by  the  Combination  of 
Hydrogen  and  Oxygen. — The  heat  evolved  when  hydrogen 
combines  with  oxygen  is  very  great,  and  it  is  utilized  for 
various  purposes.  To  burn  hydrogen  in  the  air  is,  as  we 
have  seen,  a  simple  matter,  but  to  burn  it  in  oxygen  re- 
quires a  special  apparatus  to  prevent  the  mixing  of  the 
gases  before  they  reach  the  end  of  the  tube  where  the  com- 
bustion takes  place,  The  oxyhydrogen  How-pipe  answers 
this  purpose.  It  is  simply  a  tube  with  a  smaller  tube  pass- 
ing through  it,  as  shown  in  Figure  23. 


PROPERTIES  OF  WATER.  87 

The  hydrogen  is  admitted  through  a  and  the  oxygen 
through  b.  It  will  be  seen  that  they  come  together  only  at 
the  end  of  the  tube.  The  hydrogen  is  first  passed  through 
and  lighted;  then  the  oxygen  is  passed  through  slowly,  the 
pressure  being  increased  until  the  flame  appears  thin  and 
straight.  It  gives  very  little  light,  but  is  intensely  hot. 

EXPEKIMENT  47. — Hold  in  the  flame  of  the   oxy hydro 
gen  blow-pipe  successively  a  piece  of  iron  wire,  a  piece  of  a 
steel  watch-spring,  a  piece  of  copper  wire,  a  piece  of  zinc,  a 
piece  of  platinum  wire. 

The  metal  platinum  is  used  for  many  purposes,  particn* 
larly  for  chemical  operations.  The  vessels  are  made  fron? 
molten  platinum,  and  the  metal  is  melted  by  means  of  the 
oxyhydrogen  blow-pipe. 

When  the  flame  is  allowed  to  play  upon  some  substance 
which  it  cannot  melt  nor  burn  up,  the  substance  becomes 
heated  so  high  that  it  gives  off  an  intense  light.  The  sub- 
stance commonly  used  is  quicklime.  Hence  the  light  is 
often  called  the  lime  light.  It  is  also  known  as  the 
Drummond  light. 

EXPERIMENT  48. — Cut  a  piece  of  lime  of  convenient  size 
and  shape,  say  an  inch  long  by  three  quarters  of  an  inch 
wide,  and  the  same  thickness.  Fix  it  in  position  so  that 
the  flame  of  the  oxyhydrogen  blow-pipe  will  play  upon  it. 
The  light  is  very  bright,  but  by  no  means  as  intense  as  the 
electric  light. 

Properties  of  Water.— Though,  as  we  know,  water  is 
widely  distributed  over  the  earth,  we  never  find  perfectly 
pure  water.  All  natural  waters  contain  foreign  substances 
in  solution.  These  foreign  substances  are  taken  up  from 
the  air,  or  from  the  soil.  In  order  to  get  pure  water,  it  is 
distilled.  Distillation  consists  in  boiling  the  water,  and 


88 


INTRODUCTION  TO  CHEMISTRY. 


then  condensing  the  vapor  by  passing  it  through  a  tube 
which  is  kept  cool  by  surrounding  it  with  cold  water.  A 
simple  apparatus  for  the  purpose  is  that  illustrated  in  Fig. 
24. 

The  water  to  be  distilled  is  placed  in  the  flask  A.  The 
flask  is  connected  by  means  of  a  bent  glass  tube  B  with 
the  long  tube  C  C.  This  in  turn  is  surrounded  by  the 
larger  tube  or  jacket  D.  The  side  tube  E  is  connected 


FIG.  24. 

* 

with  a  faucet  by  means  of  the  rubber  tube  0.  The  water 
is  allowed  to  flow  slowly  into  the  jacket  and  out  at  F, 
whence  it  passes  through  the  rubber  tube  H  to  the  sink. 
When  the  water  in  A  is  boiled,  the  vapor  passes  into  the 
tube  C  G.  Here  it  is  cooled  down,  and  takes  the  form  of 
liquid,  which  runs  down  and  collects  in  the  flask  K,  which 
is  called  the  receiver. 

EXPERIMENT  49. — Dissolve  some  copper  sulphate,  or 
other  colored  substance,  in  a  litre  of  water,  and  distil  the 
water. 

By  means  of  distillation  most  substances  held  in  solution 
in  water  can  be  gotten  rid  of.  Substances  which  are  vola- 
tile, however,  will  of  course  pass  over  with  the  water  vapor. 


PROPERTIES  OF  WATER.  89 

The  purest  water  found  in  nature  is  rain  water,  particu- 
larly that  which  falls  after  it  has  rained  for  some  time. 
That  which  first  falls  always  contains  impurities  from  the 
air.  As  soon  as  the  rain  water  comes  in  contact  with  the 
earth,  and  begins  its  course  towards  the  ocean,  it  begins 
to  take  up  various  substances,  according  to  the  character 
of  the  soil  with  which  it  comes  in  contact.  Mountain 
streams  which  flow  over  rocky  beds,  particularly  over  beds 
of  sandstone,  which  is  very  insoluble,  contain  exceptionally 
pure  water.  Streams  which  flow  over  limestone  dissolve 
some  of  the  stone,  and  the  water  becomes  "hard."  The 
many  varieties  of  mineral  springs  have  their  origin  in  the 
presence  in  the  earth  of  certain  substances  which  are  sol- 
uble in  water.  Common  salt  occurs  in  large  quantities  in 
different  parts  of  the  earth.  As  it  is  easily  soluble  in 
water,  many  streams  contain  it;  and  as  all  the  streams  find 
their  way  into  the  ocean,  we  see  one  reason  why  the  water 
of  the  ocean  should  be  salt.  As  streams  approach  the  habi- 
tations of  man  they  are  subjected  to  a  serious  cause  of  con- 
tamination. The  drainage  from  the  neighborhood  of  hu- 
man dwellings  is  very  apt  to  find  its  way  into  a  near  stream. 
This  condition  of  things  is  most  strjkingly  illustrated  by 
the  case  of  a  large  town  situated  on  the  banks  of  a  river.  It 
frequently  happens  that  the  water  of  the  river  is  used  for 
drinking  purposes,  and  it  also  frequently  happens  that  the 
water  is  contaminated  by  drainage.  Water  when  once  con- 
taminated by  drainage  tends  to  become  pure  again  by  con- 
tact with  the  air.  If  it  is  to  be  used  for  drinking  purposes, 
however,  it  is  not  well  to  rely  too  much  upon  thi  i  process 
of  purification. 

Pure  water  is  tasteless  and  inodorous.  In  thin  layers 
it  is  colorless,  but  in  thick  layers  it  is  blue.  This  has 


90  INTRODUCTION  TO  CHEMISTRY. 

been  shown  in  the  laboratory  by  filling  a  long  tube  with 
distilled  water.  When  looked  through  it  appears  blue. 
The  beautiful  blue  color  of  the  water  of  some  lakes  is  the 
natural  color  of  pure  water. 

On  cooling,  water  contracts  until  it  reaches  the  tempera- 
ture of  4°.  At  this  point  it  has  its  maximum  density. 
When  cooled  below  4°  it  expands,  and  the  specific  gravity 
of  ice  is  somewhat  less  than  that  of  water.  Hence  ice 
floats  on  water. 

Uses  of  Water  in  Chemistry. — Water  is  the  best  solvent. 
A  greater  number  of  substances  dissolve  in  it  than  in  any 
other  liquid.  Chemical  operations  are  very  frequently 
carried  on  in  solution.  That  is  to  say,  the  substances 
which  are  to  act  chemically  upon  one  another  are  first 
brought  into  solution.  The  object  of  this  is  to  get  the 
substances  into  as  close  contact  as  possible.  If  we  rub  two 
solids  together,  the  particles  remain  separated  by  sensible 
distances,  no  matter  how  finely  the  mixture  may  be  pow- 
dered. If,  however,  the  substances  be  dissolved,  and  the 
solutions  poured  together,  the  particles  of  the  liquid  move 
so  freely  among  one  another  that  they  come  in  intimate 
contact,  thus  facilitating  chemical  action.  In  some  cases 
substances  which  do  not  act  upon  one  another  at  all  when 
brought  together  in  dry  condition  act  readily  when  brought 
together  in  solution. 

Solution. — In  a  solution  the  par  tides -of  the  solid  dis- 
solved are  in  some  way  attracted  and  held  in  combination 
by  the  particles  of  the  liquid.  There  is  a  definite  limit  to 
the  amount  of  any  substance  which  can  thus  be  held  in  so- 
lution at  a  given  temperature.  The  substance  dissolved  is 
distributed  uniformly  through  the  solution,  no  matter  how 
dilute  or  how  concentrated  the  solution  may  be,  provided 


OZONB.  91 

it  has  stood  long  enough,  or  has  been  thoroughly  mixed  by 
stirring. 

In  representing  by  an  equation  a  reaction  which  takes 
place  between  substances  in  solution,  it  is  not  customary 
to  take  account  of  the  water,  which  mainly  plays  the  part 
of  a  solvent.  We  have  already  had  an  illustration  of  this 
in  the  case  of  hydrochloric  acid  and  zinc.  What  we  call 
hydrochloric  acid  in  the  laboratory  is  a  solution  of  the  gas, 
HC1,  in  water.  When  this  solution  is  used,  however,  it  is 
the  hydrochloric  acid  itself,  i.e.,  the  compound  HC1, 
which  acts,  while  the  role  played  by  the  water  is  secondary. 
Therefore  the  water  does  not  appear  in  the  equation: 

Zn  +  2HC1  =  ZnCl,  +  2H. 
We  might  indeed  represent  the  action  thus: 

Zn  +  2HC1  +  H20  =  ZnCl2  +  2H  +  H20, 

but  this  would  only  complicate  the  matter  without  in  any 
way  helping  us. 

Ozone. — When  electric  sparks  are  passed  for  a  time 
through  oxygen  it  undergoes  a  remarkable  change.  It  ac- 
quires a  strong  odor,  and  is  much  more  active  than  under 
ordinary  circumstances.  The  odor  of  the  gas  is  observed 
in  the  neighborhood  of  an  electric  machine  in  action,  and 
is  said  to  be  noticed  during  thunder  showers.  The  sub- 
stance which  has  the  odor  is  ozone.  It  is  formed  in  a 
number  of  chemical  reactions,  as  when  phosphorus  acts 
on  the  air  in  the  presence  of  water.  By  cold  and  pressure 
it  has  been  obtained  in  the  form  of  a  dark-blue  liquid. 

When  a  certain  volume  of  oxygen  is  converted  into 
ozone  the  volume  of  gas  is  decreased  from  three  to  two. 

By  heating  ozone  above  300°  it  is  converted  into  ordinary 
oxygen,  and  its  volume  is  increased  from  two  to  three. 


92  INTRODUCTION  TO  CHEMISTRY. 

It  is  clear  that  the  element  oxygen  can  be  converted  into 
something  else  without  the  addition  of  anything  to  it. 
This  might  lead  us  to  conclude  that  it  is  not  an  element. 
But  the  substance  formed  from  it  has  exactly  the  same 
weight  and  can  be  changed  back  again  to  oxygen  without 
anything  being  added  to  it.  It  follows  that  the  change 
must  take  place  within  the  oxygen  itself.  The  commonly 
accepted  explanation  of  the  relation  between  oxygen  and 
ozone  will  be  given  later.  (See  Chapter  XL,  Molecular 
Weights.) 

Ozone  is  present  in  small  quantity  in  the  air. 

Hydrogen  Dioxide,  H202. — Besides  water,  hydrogen  and 
oxygen  form  a  second  compound  with  each  other.  This  is 
hydrogen  dioxide,  H202.*  It  is  prepared  by  treating  barium 
dioxide,  Ba02,  with  sulphuric  acid.  The  reaction  which 
takes  place  will  be  explained  under  barium  dioxide. 

Hydrogen  dioxide  is  a  liquid  which  breaks  up  readily 
into  water  and  oxygen.  The  ease  with  which  it  gives  up 
oxygen  makes  it  a  good  oxidizing  agent.  It  is  now  manu- 
factured on  the  large  scale. 

Summary. — We  have  thus  learned  that  (1)  water  can  be 
decomposed  into  hydrogen  and  oxygen  by  means  of  an  elec- 
tric current;  (2)  the  gases  are  obtained  in  the  proportion 
of  eight  parts  by  weight  of  oxygen  to  one  part  by  weight 
of  hydrogen,  or  one  volume  of  oxygen  to  two  volumes  of 
hydrogen;  (3)  when  hydrogen  is  burned  water  is  formed; 
(4)  when  hydrogen  and  oxygen  are  mixed  together  they  do 
not  combine  under  ordinary  circumstances;  (5)  when  a 
spark  or  flame  is  brought  in  contact  with  the  mixture  vio- 
lent action  takes  place  accompanied  by  explosion;  (6)  the 

*  The  reason  for  writing  this  formula  H2O2  and  not  HO  will  Ibe 
seen  after  studying  Chapter  XI. 


COMPARISON  OF  HYDROS  KN  AND  OXYGEN.        93 

action  is  occasioned  by  the  chemical  combination  of  the 
two  gases;  (7)  they  combine  in  the  same  proportions  as 
those  in  which  they  are  obtained  from  water  by  the  action 
of  the  electric  current;  (8)  water  can  be  made  by  passing 
hydrogen  over  heated  copper  oxide;  (9)  by  weighing  the 
copper  oxide  before  and  after  the  experiment,  and  deter- 
mining the  weight  of  the  water  formed,  the  proportion  of 
water  which  consists  of  oxygen  is  found  to  be  eight  ninths. 

All  these  facts  taken  together  prove  that  the  composition 
of  water  is  what  it  has  been  stated  to  be.  Now,  using  the 
accepted  combining  weights  of  hydrogen  and  oxygen,  viz.,  1 
and  16, — the  simplest  formula  which  expresses  the  composi- 
tion of  water  is  H20.  This  expresses  the  fact  that  water 
is  composed  of  3  parts  by  weight  of  hydrogen  and  16  parts 
by  weight  of  oxygen,  or  1  part  of  the  former  to  8  of  the 
latter.  It  will  be  noticed  that  the  formula  also  indicates 
the  volumes  of  the  gases  which  enter  into  combination 
with  each  other.  Two  volumes  of  hydrogen  are  combined 
with  one  of  oxygen,  and  two  combining  weights  of  hydro- 
gen are  combined  with  one  combining  weight  of  oxygen, 
H20.  This  is,  of  course,  connected  with  the  remarkable 
fact,  to  which  attention  has  already  been  called  (see  ante, 
p.  68),  that  the  combining  weights  of  hydrogen  and  oxygen 
bear  the  same  relation  to  each  other  that  the  absolute 
weights  of  equal  volumes  of  the  gases  do. 

Comparison  of  Hydrogen  and  Oxygen. — Hydrogen  an<! 
oxygen  are  different  kinds  of  matter,  just  as  heat  and 
electricity  are  different  kinds  of  energy.  Heat  can  be  con- 
verted into  electricity,  and  electricity  into  heat,  but  one 
element  cannot  by  any  means  known  to  us  be  converted  into 
another.  They  are  apparently  entirely  independent  of  each 
other.  The  question  will  therefore  suggest  itself,  whether, 


94  INTRODUCTION  TO  CHEMISTRY. 

in  spite  of  their  apparent  independence,  there  is  not  some 
relation  between  the  different  elements  which  reveals  it- 
self by  similarity  in  properties  ?  It  will  be  found  that  the 
elements  can  be  divided  into  groups  or  families  according  to 
their  properties.  There  are  some  elements,  for  example, 
which  in  their  chemical  conduct  resemble  oxygen  markedly. 
These  elements  make  up  the  oxygen  family.  So  far  as  hy- 
drogen is  concerned,  however,  it  stands  by  itself.  There 
is  no  other  element  which  conducts  itself  like  it.  If  we 
compare  it  with  oxygen,  we  find  very  few  facts  which  indi- 
cate any  analogy  between  the  two  elements.  In  their  phys- 
ical properties  they  are,  to  be  sure,  similar.  Both  are  trans- 
parent, colorless,  inodorous  gases.  On  the  other  hand, 
oxygen  combines  readily  with  a  large  number  of  substances 
with  which  hydrogen  does  not  combine.  Oxygen,  as  we 
have  seen,  combines  easily  with  carbon,  sulphur,  phos- 
phorus, and  iron.  It  is  a  difficult  matter  to  get  any  of 
these  elements  to  combine  directly  with  hydrogen.  Further 
than  this,  substances  which  combine  readily  with  hydrogen 
do  not  combine  readily  with  oxygen.  The  two  elements 
exhibit  opposite  chemical  properties.  What  one  can  do, 
the  other  cannot  do.  Thisoppositeness  of  properties  is  fa- 
vorable to  combination  ;  for  not  only  do  hydrogen  and  oxy- 
gen, with  their  opposite  properties,  combine  with  great  ease 
under  the  proper  conditions,  but,  as  we  shall  see  later,  it 
is  a  general  rule  that  elements  of  like  properties  do  not 
readily  combine  with  one  another,  while  elements  of  unlike 
properties  do  readily  combine  with  one  another. 

"We  shall  next  take  up  the  study  of  a  third  element,  which 
is  widely  distributed  in  nature,  which  in  some  respects  re- 
sembles both  hydrogen  and  oxygen,  and  in  some  respects 
differs  from  each.  This  is  the  element  chlorine. 


CHAPTER  V. 

CHLORINE    AND    ITS    COMPOUNDS  WITH    HYDROGEN 
AND  OXYGEN. 

Occurrence. — Chlorine,  though  widely  distributed  in  na- 
ture, does  not  occur  in  very  large  quantity  as  compared 
with  oxygen  and  hydrogen.  It  is  found  chiefly  in  combi- 
nation with  the  element  sodium  as  common  salt,  or  sodium 
chloride,  which  has  the  composition  represented  by  the 
formula  NaCl.  It  is  also  found  in  combination  with  other 
elements,  as  potassium,  magnesium,  etc.  In.  comparatively 
small  quantity  it  occurs  in  combination  with  silver,  form- 
ing one  of  the  most  valuable  silver  ores.  All  the  chlorine 
with  which  we  have  to  deal  is  made  from  common  salt. 

Preparation. — It  is  not  practicable  to  decompose  sodium 
chloride  directly  into  its  elements.  In  order  to  get  the 
chlorine  out  of  the  compound  in  the  free  state,  it  is  neces- 
sary, first,  to  get  it  in  combination  with  hydrogen  in  the 
form  of  hydrochloric  acid,  HC1.  This  is  very  easily  ac- 
complished by  treating  salt  with  ordinary  sulphuric  acid. 
When  the  two  are  brought  together  a  change  takes  place, 
which  will  be  studied  more  in  detail  farther  on.  The  re- 
action is  represented  thus  : 

(1)  2NaCl  +  H2S04  =  Na2S04  +  2HC1. 

As  will  be  seen,  the  sodium  of  the  sodium  chloride  and 
the  hydrogen  of   the  hydrochloric  acid  exchange   places, 


96  INTRODUCTION  TO  CHEMISTRY. 

a  kind  of  action  which  is  quite  common.  This  particular 
reaction  is  of  very  great  importance  in  the  arts,  as  it  is  the 
first  stage  in  the  preparation  of  common  "  soda"  or  sodium 
carbonate,  and  of  chlorine. 

Now,  if  hydrochloric  acid  be  brought  in  contact  with  a 
substance  which  gives  up  oxygen  easily,  the  hydrogen  will 
unite  with  the  oxygen  to  form  water,  and  the  chlorine  will 
be  set  free.  The  reaction  is  expressed  thus: 

(2)  2HC1  +  0  =  H20  +  201. 

[PROBLEM. — How  much  sulphuric  acid  will  it  require  to  set  free 
enough  hydrochloric  acid  to  make  25  grams  of  chlorine?] 

As  we  have  an  unlimited  supply  of  oxygen  in  the  air,  it 
would  be  advantageous  could  we  effect  the  decomposition 
of  hydrochloric  acid  by  means  of  the  element  in  the  free 
state.  On  the  large  scale  this  is  now  accomplished.  Dea- 
con's process  for  manufacturing  chlorine  consists  in  passing 
air  and  hydrochloric  acid  together  through  a  heated  tube 
containing  clay  balls  saturated  with  copper  sulphate.  Ex- 
actly^why  the  oxidation  takes  place  under  these  circum- 
stances is  not  known.  The  essential  feature  of  the  reac- 
tion is  nevertheless  the  oxidation  of  the  hydrochloric  acid, 
as  represented  in  equation  (2). 

For  the  preparation  of  chlorine  in  the  laboratory  it  is 
most  convenient  to  bring  hydrochloric  acid  in  contact  with 
manganese  dioxide,  Mn02,  a  substance  which  we  have  al- 
ready had  to  deal  with  for  the  purpose  of  preparing  oxygen. 
The  action  which  takes  place  is  explained  thus:  In  the 
first  place,  when  hydrochloric  acid  acts  upon  some  com- 
pounds containing  oxygen,  the  hydrogen  and  oxygen  com- 
bine, and  the  element  which  was  in  combination  with  oxy- 
gen combines  with  chlorine.  Thus,  when  the  compound 


PREPARATION  OF  CHLORINE.  97 

MnO  is  treated  with  hydrochloric  acid,  this  reaction  takes 
place • 

MnO  -f  2HC1  =  MnOl,  +  HaO. 

So,  also>  when  manganese  dioxide  is  treated  with  hydro- 
chloric  acid,  the  oxygen  is  probably  first  replaced  by  chlo- 
rine, 'as  represented  in  the  equation 

MnOa  +  4H01  =  MnCl4  +  2H30. 

But  the  compound  Mn014  gives  up  half  of  its  chlorine 
when  heated: 

Mn014  =  MnOl,  +  201. 

So  that  the  action  of  hydrochloric  acid  on  manganese  di- 
oxide is  represented  as  follows: 

Mn02  +  4H01  =  Mn013  -f  2HaO  +  20L 

[PROBLEM. — How  much  manganese  dioxide  would  be  required  to 
liberate  50  grams  of  chlorine  ?  The  combining  weight  of  manga- 
nese is  55.] 

Instead  of  first  making  the  hydrochloric  acid  from  salt 
and  then  treating  the  hydrochloric  acid  with  manganese 
dioxide,  it  is  really  best  to  mix  together  the  manganese  di- 
oxide and  common  salt  and  pour  upon  the  mixture  the 
necessary  quantity  of  sulphuric  acid.  For  practical  pur- 
poses mix  5  parts  of  coarsely  granulated  manganese  diox- 
ide and  5  parts  of  coarsely  granulated  common  salt.  Make 
a  mixture  of  12  parts  of  concentrated  sulphuric  acid  and  6 
parts  of  water.  *  Let  this  mixture  cool  down  thoroughly, 
and  then  pour  it  upon  the  mixture  of  salt  and  manganese 
dioxide.  Gently  heat,  and  a  regular  current  of  chlorine 
will  be  given  off.  This  is  by  far  the  best  way  to  make 
chlorine  in  the  laboratory. 

In  this  case  the  manganese  dioxide  and  sulphuric  acid 
give  off  oxygen,  and  the  common  salt  and  sulphuric  acid 

*  See  precautions  necessary  noted  on  p.  64. 


98  INTRODUCTION  TO  CHEMISTRY. 

give  off  hydrochloric  acid.     The  oxygen  then  oxidizes  the 
hydrochloric  acid,  and  chlorine  is  given  off. 

EXPERIMENT  50. — Pour  2  or  3  cc.  concentrated  sulphu- 
ric acid  on  a  gram  or  two  of  common  salt  in  a  test-tube. 
A  gas  will  be  given  off  which  forms  dense  white  fumes  in 
the  air  and  has  a  sharp,  penetrating  taste  and  smell.  This 
is  hydrochloric  acid  gas* 

EXPERIMENT  51. — Pour  2  or  3  cc.  concentrated  sulphu- 
ric acid  on  a  few  grams  of  manganese  dioxide  in  a  test-tube. 
Heat,  and  examine  the  gas  given  off.  Convince  yourself 
that  it  is  oxygen. 

EXPERIMENT  52. — Mix  2  grams  manganese  dioxide  and 
2  grams  common  salt.  Pour  4  to  5  cc.  sulphuric  acid  on 
the  mixture  in  a  test-tube.  This  experiment  should  be 
performed  under  a  hood  in  which  the  draught  is  good,  as 
the  gas  which  is  given  off  is  not  only  very  disagreeable, 
but  very  irritating  to  the  respiratory  organs.  Notice  the 
color  and  odor  of  the  gas.  [Does  it  support  combustion? 
Does  it  burn?] 

Properties. — Chlorine  is  a  greenish-yellow  gas.  It  has  a 
disagreeable  smell,  and  acts  upon  the  passages  of  the  throat 
and  nose,  causing  irritation  and  inflammation.  The  effect 
is  much  like  that  of  "  a  cold  in  the  head."  Inhaled  in  con- 
centrated form,  i.e.,  not  diluted  with  a  great  deal  of  air, 
it  would  cause  death.  It  is  much  heavier  than  air,  its  spe- 
cific gravity  being  2.45.  A  litre  of  chlorine  gas,  under 
standard  conditions,  weighs  3.167  grams.  It  is  soluble  in 
water  and  acts  upon  mercury,  and  therefore  cannot  be  col- 
lected by  displacement  of  either  of  these  liquids.  The  most 
convenient  way  to  collect  it  is  by  displacement  of  air.  The 
apparatus  for  the  purpose  is  arranged  as  shown  in  Fig.  25. 

The  delivery-tube  should  extend  to  the  bottom  of  the  col- 


PROPERTIES  OF  CHLORINE. 


99 


lecting  vessel.  This  vessel  should  be  dry,  and  its  mouth 
covered  with  a.  piece  of  paper  to  prevent  currents  of  air 
from  carrying  away  the  chlorine.  As  the  gas  collects  in 
the  vessel  the  experimenter  can  judge  of  the  quantity  pres- 
ent by  the  color. 


Fio.  25. 

EXPEKIMENT  53.— Collect  six  or  eight  dry  cylinders  or 
bottles  full  of  chlorine.  Make  the  gas  from  about  100 
grams  of  manganese  dioxide,  using  the  other  substances 
in  the  proportions  already  stated. 

(1)  Introduce  into  one  of  the  vessels  containing  chlorine 
a  little  finely  powdered  antimony.  The  two  elements  com- 


100  INTRODUCTION  TO  CHEMISTRY. 

bine  at  once  with  evolution  of  light.     The  product  is  anti 
mony  trichloride,  Sb013. 

[In  what  respects  does  this  experiment  resemble  the  one 
in  which  iron  was  burned  in  oxygen?  In  what  respects  do 
the  two  differ?] 

(2)  Into  a  second  vessel  introduce  a  few  pieces  of  heated 
thin  copper  foil.     Combination  takes   place  with   evolu- 
tion of  light  and  heat. 

(3)  Into  a  third  vessel  introduce  a  piece  of  paper  with 
some  writing   on  it,  some  flowers,  and  pieces  of  colored 
calico.     Most  of  the  colors  will  be  destroyed  if  the  substan- 
ces are  moist. 

(4)  Into  a  fourth  vessel  introduce  a  dry  piece  of  the  same 
colored  calico  as  that  used  in  the  previous  experiment. 
The  dry  piece  is  not  bleached.     The  moist  piece  is. 

From  these  experiments  we  learn  that  chlorine  com- 
bines readily  with  other  substances,  and  also  that  it  de- 
stroys colors  or  bleaches.  It  is  indeed  one  of  the  most 
active  elements.  It  not  only  .acts  directly  upon  many  of 
the  elements  at  ordinary  temperatures,  and  decomposes 
many  compounds,  but  it  also  acts  upon  most  organic  sub- 
stances, or  such  as  are  formed  as  the  products  of  animal  or 
vegetable  life.  Its  action  upon  the  tissues  of  the  respira- 
tory organs  has  already  been  noticed. 

EXPERIMENT  54. — Out  a  piece  of  filter-paper  about  an 
inch  wide  and  six  to  eight  inches  long.  Pour  on  this  some 
ordinary  oil  of  turpentine  previously  warmed  slightly.  In- 
troduce this  into  the  sixth  vessel  of  chlorine.  A  flash  of 
flame  is  noticed  and  a  dense  cloud  of  black  smoke  is 
formed.  The  action  here  is  due  to  the  great  affinity  of 
chlorine  for  hydrogen.  Oil  of  turpentine  consists  of  car- 
bon and  hydrogen.  The  main  action  of  the  chlorine  con- 


A  GTION'OF  JCMLtitiW1SJ  ON 'WA fig!. '  '''         1Q1 

sists  in  extracting  the  hydrogen  and  leaving  the  carbon. 
The  experiment  is  interesting  chiefly  in  so  far  as  it  illus- 
trates the  general  tendency  of  chlorine  to  act  upon  vegeta- 
ble substances. 

It  was  noticed  that  when  moisture  is  present  chlorine 
bleaches,  while  when  it  is  not  present  bleaching  does  not 
take  place.  The  reason  of  these  facts  is  interesting. 
Chlorine  acts  directly  upon  some  dye-stuffs,  converting 
them  into  colorless  substances.  In  other  cases  it  has  been 
shown  that  the  destruction  of  the  color  is  due  to  oxygen, 
which  is  set  free  from  water  by  the  action  of  chlorine.  In 
the  direct  sunlight  chlorine  decomposes  water  according  to 

this  equation: 

201  +  H20  =  2HC1  +  0. 

EXPERIMENT  55. — Seal  the  end  of  a  glass  tube  about  a 
metre  (or  about  a  yard)  long  and  about  12 
mm.  (-J  inch)  internal  diameter.  Fill  this 
with  a  strong  solution  of  chlorine  in  water. 
Invert  it,  as  shown  in  Fig.  26,  in  a  shallow 
vessel  containing  some  of  the  same  solution 
of  chlorine  in  water.  Place  the  tube  in  di- 
rect sunlight.  Gradually  bubbles  of  gas  will 
be  seen  to  rise  and  collect  in  the  upper  end, 
and  the  color  of  the  solution,  which  is  at  first 
greenish-yellow,  like  that  of  chlorine,  disap- 
pears. The  gas  can  be  shown  to  be  oxygen. 

In  bleaching,  this  decomposition  of  water 
takes  place  in  direct  contact  with  the  colored 
materials,  and  the  oxygen,  the  instant  it  is 
set  free,  is  more  active  than  free  oxygen  is. 
It  is  this  oxygen  which  is  being  set  free  which    Sl§!liJP 
acts  upon  the  colored  substances  and  converts        FIG.  2G. 
them  into  colorless  substances. 


102  LI  WTltOtifrCTIOl?  TO  CHEMISTRY. 

Chlorine  Hydrate. — When  chlorine  gas  is  passed  hit* 
water  cooled  down  almost  to  the  freezing  point,  crystals 
appear  in  the  vessel.  These  consist  of  chlorine  and  water 
and  are  known  as  chlorine  hydrate.  Its  composition  is 
represented  by  the  formula  Cl  -f  5H20.  The  crystals  are 
very  unstable,  breaking  up  at  the  ordinary  temperature 
into  chlorine  gas  and  water. 

The  ease  with  which  chlorine  decomposes  water  and 
vegetable  substances  containing  hydrogen  shows  that  it  has 
a  strong  affinity  for  hydrogen.  Just  as  hydrogen  burns  in 
oxygen,  it  also  burns  in  chlorine. 

EXPERIMENT  56.— Light  a  jet  of  hydrogen  in  the  air 
and  carefully  introduce  it  into  a  vessel  containing  chlo- 
rine. It  will  continue  to  burn,  but  the  flame  will  not  ap- 
pear the  same.  A  gas  will  be  given  off  which  forms  clouds 
in  the  air.  This  gas  has  a  sharp,  penetrating  taste  and 
smell. 

The  burning  of  hydrogen  in  air  or  oxygen  is  simply  "the 
act  of  combination  of  hydrogen  and  oxygen,  the  product 
being  water  in  the  state  of  vapor,  and  therefore  invisible. 
When  hydrogen  burns  in  chlorine  the  action  consists  in 
the  union  of  the  two  gases,  the  product  being  hydrochloric 
acid,  HC1,  which  forms  the  clouds  in  the  air.  In  both 
cases  the  action  is  accompanied  by  an  evolution  of  heat 
and  light. 

Just  as  the  compounds  of  oxygen  with  other  elements 
are  called  oxides,  so  the  compounds  of  chlorine  with  other 
elements  are  called  chlorides.  We  distinguish  between  the 
different  chlorides  in  the  same  way  that  we  distinguish  be- 
tween the  different  oxides  (see  p.  57). 

Hydrochloric  Acid. — The  only  compound  which  chlorine 
and  hydrogen  form  with  each  other  is  hydrochloric 


BYDHOCHLORIC  ACID.  103 

acid.  It  has  already  been  shown  that  hydrogen  burns 
in  chlorine  and  that  hydrochloric  acid  is  formed.  The 
two  gases  may  be  mixed  together  and  allowed  to  stand 
together  indefinitely  in  the  dark  and  no  action"  will  take 
place.  If,  however,  the  mixture  be  put  in  diffused  sun- 
light, gradual  combination  takes  place;  and  if  the  direct 
light  of  the  sun  be  allowed  to  shine  for  an  instant  on  the 
mixture,  explosion  occurs,  and  this  is  the  sign  of  the  com- 
bination of  the  two  gases.  The  same  sudden  combination 
is  effected  by  applying  a  flame  or  spark  to  the  mixture,  or 
by  illuminating  it  instantaneously  with  the  light  from  a 
piece  of  burning  magnesium  or  electric  light. 

[What  difference  is  there  between  the  combination  of  hy- 
drogen and  oxygen  and  of  hydrogen  and  chlorine?] 

The  way  in  which  the  sunlight  and  other  bright  lights 
act  upon  the  mixture  of  hydrogen  and  chlorine  to  cause 
them  to  combine  is  not  understood;  but  the  fact  that  sun- 
light does  have  a  marked  influence  upon  some  kinds  of 
chemical  action  is  well  known.  One  other  illustration  of 
this  influence  has  already  been  before  us,  that  of  the  de- 
composition of  water  by  chlorine.  This  action  does  not 
take  place  in  the  dark.  The  sunlight  is  essential.  The 
arfc  of  photography  is  based  upon  the  influence  of  light  in 
causing  chemical  changes.  The  light  from  the  object 
photographed  is  allowed  to  act  in  the  camera  on  a  plate, 
upon  the  surface  of  which  is  a  substance  which  is  changed 
chemically  by  light.  It  should  be  specially  noted  that  the 
cause  of  the  chemical  changes  in  these  cases  is  not  the 
heat  but  the  light.  If  the  substances  are  heated  to  the 
same  temperature  in  the  dark,  the  changes  do  not  take 
place. 

Preparation. — To  prepare  hydrochloric  acid,  common 
salt  or  sodium  chloride,  NaOl,  is  treated  with  sulphuric 


104  INTRODUCTION  TO  CHEMISTRY. 

acid  (see  Experiment  50,  p.  97).  As  has  already  been  ex- 
plained, the  hydrogen  of  the  sulphuric  acid  and  the  sodium 
of  the  salt  exchange  places,  as  represented  in  the  equation 

SNaCl  +  H2S04  =  Na2S04  -f  2HC1. 

The  products  are  sodium  sulphate  and  hydrochloric  acid. 
The  hydrochloric  acid  is  given  off  as  a  gas,  and  the  sodium 
sulphate  remains  behind  in  the  flask. 

Properties.— Hydrochloric  acid  is  a  colorless  transparent 
gas.  It  has  a  sharp  penetrating  taste  and  smell.  If  inhaled 
into  the  lungs  it  produces  suffocation.  It  dissolves  in  water 
very  readily.  At  ordinary  temperatures  one  volume  of 
water  will  dissolve  450  times  its  own  volume  of  the  gas. 
The  solution  is  the  liquid  known  in  the  laboratory  as  hy- 
drochloric acid. 

[PROBLEM. — A  litre  of  hydrochloric  acid  gas  weighs  1.6283  grams 
at  0°.  At  0°  one  volume  of  water  will  absorb  500  times  its  own 
volume  of  the  gas.  How  much  will  a  litre  of  water  increase  in 
weight  at  0°  by  taking  up  all  the  hydrochloric  acid  it  can?] 

So  strong  is  the  attraction  of  hydrochloric  acid  for  water 
that  it  condenses  moisture  from  the  air;  hence,  although 
the  gas  itself  is  quite  colorless  and  transparent,  when  it 
comes  in  contact  with  the  air  dense  white  clouds  are 
formed,  which  are  not  formed  if  it  is  kept  from  contact 
with  the  air. — Hydrochloric  acid  does  not  burn  and  docs 
not  support  combustion.  This  is  equivalent  to  saying  that 
it  does  not  combine  with  oxygen  under  ordinary  circum- 
stances, and  that  substances  which  combine  with  the  oxy- 
gen of  the  air  do  not  combine  with  hydrochloric  acid. 

[What  evidence  have  we  had  that,  under  some  circum- 
stances, oxygen  does  act  on  hydrochloric  acid  ?  What  are 
the  circumstances?  What  are  the  products?] 

Commercial  hydrochloric  acid  is  a  yellowish  liquid,  the 
color  being  due  to  the  presence  of  impurities.  The  solu- 
tion is  obtained  in  the  factories  in  which  "  soda,"  or  sodium 


&YDEOCIlLOmC  ACID.  105 

carbonate  is  made.  This  is  an  extremely  important  sub- 
stance in  the  arts.  It  does  not  occur  in  nature,  but  is 
manufactured  from  common  salt.  In  the  process  most 
commonly  used  the  salt  is  first  converted  into  sodium 
sulphate  by  treating  it  with  sulphuric  acid.  Hydrochloric 
acid  is  necessarily  given  off.  When  the  factories  were  first 
established  in  England,  the  gas  was  allowed  to  escape  as  a 
waste  product,  but  the  effects  produced  by  it  upon  the 
vegetation  of  the  surrounding  country  were  so  destructive 
that  a  law  was  passed  prohibiting  the  manufacturers  from 
allowing  the  gas  to  escape.  It  is  now  collected  by  passing 
it  through  water.  Thus  enormous  quantities  of  the  solu- 
tion are  produced,  but  its  uses  are  numerous  and  it  always 
commands  a  price. 

Pure  hydrochloric  acid  is  a  solution  of  the  pure  gas  in 
pure  water.  It  is  colorless,  and  when  concentrated  it  gives 
off  fumes  when  exposed  to  the  air.  The  solution  when 
heated  gives  off  a  large  part  of  the  gas  contained  in  it,  and 
by  boiling  it  can  all  be  evaporated. 

EXPERIMENT  57. — Arrange  an  apparatus  as  shown  in 
Fig.  27. 

Weigh  out  5  parts  common  salt,  5  parts  concentrated 
sulphuric  acid,  and  1  part  water.  Mix  the  acid  and  water, 
taking  the  usual  precautions  ;  let  the  mixture  cool  down  to 
the  ordinary  temperature  ;  and  then  pour  it  on  the  salt  in 
the  flask.  For  the  purposes  of  the  experiment  take  about  100 
grams  of  salt.  Now  heat  the  flask  gently,  and  the  gas  will  be 
regularly  evolved.  Conduct  it  at  first  through  water  con- 
tained in  the  three  Wolff's  bottles  until  what  passes  over  is  all 
absorbed  in  the  first  Wolff's  bottle.  The  reason  why  gas  at 
first  bubbles  through  all  the  bottles  is,  that  the  apparatus  is 
full  of  air,  which  is  first  driven  out.  When  the  air  has  been 


106  INTRODUCTION  TO  CHEMISTRY. 

displaced, the  gas  is  all  absorbed  as  soon  as  it  comes  in  contact 
with  the  water. — After  the  gas  has  passed  for  ten  to  fifteen 
minutes,  disconnect  at  A.  Notice  the  fumes.  These  become 
denser  by  blowing  the  breath  on  them,  as  this  increases  the 
moisture  in  the  vicinity. — Apply  a  lighted  match  to  the 
end  of  the  tube.  The  gas  does  not  burn. — Collect  some  of 
the  gas  in  a  dry  cylinder  by  displacement  of  air,  as  in  the 
case  of  chlorine.  The  specific  gravity  of  the  gas  being  1.26, 
the  vessel  must  of  course  be  placed  with  the  mouth  up- 


FIG.  27. 

ward.  That  the  gas  is  colorless  and  transparent  is  shown 
by  the  appearance  of  the  generating  flask,  which  is  filled  with 
the  gas.  Insert  a  burning  stick  or  candle  in  the  cylinder 
filled  with  the  gas.  It  is  extinguished. — Reconnect  the 
generating-flask  with  the  series  of  bottles  containing  water, 
and  let  the  process  continue  until  no  more  gas  comes  over. 
The  reaction  represented  in  the  equation 

2NaCl  +  H8S04  =  Na2S04  +  2HC1 

is  now  complete.  After  the  flask  has  cooled  down,  pour 
water  on  the  contents;  and  when  the  substance  is  dissolved 


HYDROCHLORIC  ACID.  107 

filter  it  and  evaporate  to  such  a  concentration  that,  on  cool- 
ing, the  sodium  sulphate  is  deposited.  Pour  off  the  liquid 
and  dry  the  solid  substance  by  placing  it  upon  folds  of  filter- 
paper.  Compare  the  substance  with  the  common  salt 
which  you  put  in  the  flask  before  the  experiment.  What 
proofs  have  you  that  the  two  substances  are  not  the  same  ? — 
Heat  a  small  piece  of  each  in  a  dry  tube  closed  at  one  end. 
What  differences  do  you  notice  ? — Treat  a  small  piece  of 
each  in  a  test-tube  with  sulphuric  acid.  What  difference 
do  you  notice  ? — If  in  the  experiment  we  should  recover  all 
the  sodium  sulphate  formed,  how  much  would  we  have  ? — 
Put  about  50  cc.  of  the  liquid  from  the  first  Wolff's  bottle 
in  a  porcelain  evaporating-dish.  Heat  over  a  small  flame 
just  to  boiling.  Is  hydrochloric  acid  given  off?  Can  all  the 
liquid  be  driven  off  by  boiling  ? — Try  the  action  of  the  so- 
lution on  some  iron  filings.  Is  hydrogen  given  off  ? — Add 
some  to  a  little  granulated  zinc  in  a  test-tube.  Is  hydro- 
gen given  off  ? — Add  a  little  to  some  manganese  dioxide  in 
a  test-tube.  Is  chlorine  given  off  ? — Add  ten  or  twelve 
drops  of  the  acid  to  2  to  3  cc.  water  in  a  test-tube.  Taste 
the  dilute  solution.  It  has  what  is  called  a  sour  or  acid 
taste,  the  two  terms  being  practically  synonymous. — Add  a 
drop  or  two  of  a  solution  of  Uue  litmus,  or  put  into  it 
a  piece  of  paper  colored  Uue  with  litmus.  The  color  is 
changed  to  red.  Litmus  is  a  vegetable  color  prepared  for 
use  as  a  dye.  Other  vegetable  colors  are  changed  by  hydro- 
chloric acid. — Steep  a  few  leaves  of  red  cabbage  in  water. 
Add  a  few  drops  of  the  solution  thus  obtained  to  dilute 
hydrochloric  acid.  Is  there  any  change  in  color  ? — The 
color  will  be  restored  in  each  case  by  adding  a  few 
drops  of  a  solution  of  caustic  soda. — In  what  experiment 
has  caustic  soda  been  obtained  ?  What  relation  does  it  bear 


108  INTRODUCTION  TO  CHEMISTRY. 

to  water  ? — To  the  dilute  solution  of  hydrochloric  acid  add 
drop  by  drop  a  dilute  solution  of  caustic  soda.  Is  the  acid 
taste  destroyed  ? 

\J  Analysis  of  Hydrochloric  Acid. — The  determination  of 
the  composition  of  hydrochloric  acid  is  not  as  easily  made 
as  that  of  water.  That  it  consists  of  hydrogen  and  chlorine 
is  shown  by  the  fact  that  it  is  formed  by  direct  combination 
of  these  elements.  To  determine  the  relative  weights  and 
volumes  of  the  gases  which  enter  into  combination,  we  may 
proceed  thus  :  Enclose  a  suitable  quantity  of  the  gas  in  a 
tube.  Introduce  a  small  piece  of  the  metal  potassium. 
Decomposition  will  take  place  as  represented  in  the  equa- 
tion 

K  +  HC1  =  KC1  +  H. 

The  gas  left  over  is  hydrogen.  On  measuring  its  volume 
it  v/ill  be  found  to  be  just  half  that  of  the  hydrochloric 
acid  decomposed.  The  weight  of  the  hydrogen  obtained 
will  be  found  to  bear  to  the  weight  of  the  hydrochloric 
acid  the  proportion  1:36.5.  In  other  words,  in  36.5 
parts  of  hydrochloric  acid  there  are  35.5  parts  of  chlorine 
and  1  part  of  hydrogen.  In  1  volume  of  the  gas  there 
is \  volume  of  hydrogen.  -By  mixing  equal  volumes  of  hydro- 
gen and  chlorine  and  causing  them  to  combine  it  has  been 
found  that  1  volume  of  hydrogen  combines  with  1  volume 
of  chlorine  to  form  2  volumes  of  hydrochloric  acid.  The 
specific  gravity  of  the  relative  weights  of  equal  volumes  of 
hydrogen  and  chlorine  are,— hydrogen,  0.0691;  chlorine, 
2.45.  These  figures  bear  to  each  other  the  same  relation 
as  the  combining  weights  of  the  elements,  viz.,  1  :35.5. 
[What  fact  of  the  same  kind  was  noticed  in  comparing  the 
specific  gravities  of  hydrogen  and  oxygen  ?]  Regarding 


PROPERTIES  OF  UTDROGHLOIIIG  ACID.         109 

the  chemical  conduct  of  hydrochloric  acid,  we  have  learned 
from  the  experiments  already  performed: 

1.  That  it  gives  up  its  hydrogen  when  brought  in  contact 
with  certain  substances  like  iron,  zinc,  etc.,  which  belong 
to  the  class  called  metals;  and  that  it  takes  up  the  metals 
in  place  of  the  hydrogen.  Thus  zinc  and  hydrochloric  acid 
give  zinc  chloride  and  hydrogen: 


Zn  +  mCl  =  ZnCl,  +  2H. 

2.  That  in  contact  with  substances  which  give  off 
oxygen,  or  with  oxygen  itself  under  certain  circumstances, 
it  gives  up  its  chlorine,  while  the  hydrogen  combines  with 
oxygen  to  form  water. 

We  shall  learn  hereafter  that  when  it  acts  upon  the 
compounds  of  the  metals  with  oxygen  or  the  so-called 
metallic  oxides  like  magnesia  or  magnesium  oxide,  MgO; 
lime  or  calcium  oxide,  CaO;  zinc  oxide,  ZnO,  etc.,  —  com- 
pounds which  do  not  easily  give  up  oxygen,  —  the  hydrogen 
of  the  acid  combines  with  the  oxygen  of  the  oxide  to  form 
water,  while  the  metals  combine  with  the  chlorine: 

MgO  +2IIC1  =  Mg012  +  H.O. 
CaO  +  2HC1  =  CaCl,  +  H20. 
ZnO  +  2HC1  =  ZnOl,  +  H20. 

It  will  be  noticed  that  when  hydrochloric  acid  acts  upon 
zinc  oxide  zinc  chloride  is  formed.  But  this  is  the  prod- 
uct obtained  when  hydrochloric  acid  acts  upon  the  metal 
zinc.  The  metals  calcium  and  magnesium  act  towards 
hydrochloric  acid  the  same  as  zinc.  Plainly  the  cause 
of  these  reactions,  is  the  strong  attraction  of  chlorine  for 
the  metals. 


110  INTRODUCTION  TO  CHEMISTRY. 

Compounds  of  Chlorine  with  Oxygen  and  with  Hydrogen 
and  Oxygen.  —  As  we  have  seen,  chlorine  combines  vory 
readily  with  hydrogen,  and  hydrogen  with  oxygen,  and  the 
products  are  stable  compounds.  On  the  other  hand,  chlo- 
rine cannot  be  made  to  combine  directly  with  oxygen.  By 
indirect  processes  they  can  be  combined,  but  the  com- 
pounds undergo  decomposition  easily,  yielding  back  the 
chlorine  and  oxygen  contained  in  them.  Before  consider- 
ing these  compounds  it  will  be  best  to  consider,  as  far  as 
may  be  necessary,  the  compounds  of  chlorine,  hydrogen, 
and  oxygen  which  are  more  easily  made,  and  from  which 
the  oxides  are  made. 

Compounds  of  Chlorine  with  Hydrogen  and  Oxygen.  — 
One  of  the  principal  reactions  made  use  of  for  the  prepa- 
ration of  compounds  of  chlorine,  oxygen,  and  hydrogen 
consists  in  treating  caustic  potash,  or  potassium  hydroxide, 
KOH,  with  chlorine.  We  have  learned  that  chlorine  has  a 
strong  affinity  for  metals.  Now,  if  chlorine  is  brought 
together  with  potassium  hydroxide  we  would  expect  it  to 
combine  with  the  potassium  thus: 


But  its  strong  affinity  for  hydrogen  would  cause  the  two  to 
unite,  so  that  the  result  would,  in  the  first  stage,  be  repre- 
sented thus: 

KOH  +  201  =  KC1  +  HC1  +  0. 

The  oxygen,  however,  can  combine  with  potassium  chlo- 
ride, KC1,  to  form  compounds  KC10,  KC102,  KC103,  and 
K0104;  and  the  hydrochloric  acid  formed  would  combine 
with  potassium  hydroxide  thus: 

KOH  +  HC1  =  KC1  +  H20. 
By  treating  potassium  hydroxide  with  chlorine  we  may 


OHLORINE  ACIDS. 

therefore  expect  to  obtain  potassium  chloride,  KC1;  some 
compound  of  potassium  chloride  with  oxygen;  and  water. 
The  above  equations  are  given  with  the  view  of  making 
clear^  what  actually  takes  place,  as  has  been  shown  by  exper- 
iment. The  products  are  different  according  to  circum- 
stances. If  the  solution  of  caustic  potash  is  warm  and 
concentrated  the  reaction  takes  place  as  represented,  thus: 

6KOH  +  601  =  5KC1  +  KC108  +  3H30. 

A  part  of  the  potassium  chloride  is  oxidized  to  the  form 
KC103,  which  is  known  as  potassium  chlorate. 

If,  however,  the  solution  is  dilute,  the  reaction  takes  place 
thus  : 

2KOH  +  201  =  KOI  +  KC10  +  HaO. 

In  the  latter  case  the  oxidation  of  the  potassium  chloride 
is  not  carried  as  far  as  in  the  former.  The  product  KC10 
is  known  as  potassium  hypochlorite. 

Potassium  chlorate,  KC10S,  and  potassium  hypochlorite, 
KC10,  bear  the  same  relation  to  two  compounds,  HC108 
and  HC10,  as  potassium  chloride,  KOI,  bears  to  hydrochlo- 
ric acid,  HC1,  or  sodium  chloride,  NaCl,  to  hydrochloric 
acid.  But  we  have  seen  that  hydrochloric  acid  can  be  very 
easily  obtained  from  sodium  chloride  by  simply  adding  sul- 
phuric acid.  Potassium  chloride  undergoes  the  same 
change  when  treated  with  sulphuric  acid.  Indeed,  we 
shall  see  that  nearly  all  compounds  containing  sodium  or 
potassium  give  up  these  metals  when  treated  with  sulphuric 
acid,  and  take  up  hydrogen  in  the  place  of  them. 

Treating  potassium  chloride  with  sulphuric  acid  this  re- 
action takes  place  : 

2KC1  +  H8S04  =  K,S04  +  2H01. 


112  INTRODUCTION  TO  CHEMISTRY. 

Similarly  treating  potassium  chlorate  with  sulphuric  acid, 
this  reaction  takes  place  : 

2KC10,  +  H2S04  =  K2S04  +  2HC10,. 

The  products  are  potassium  sulphate  and  chloric  acid, 
HC103.  The  chloric  acid,  however,  is  very  unstable,  and 
decomposes,  yielding  other  compounds  of  chlorine.  The 
acid  itself  can  be  made  by  taking  proper  precautions,  but 
the  chief  interest  connected  with  it  is  the  fact  that  it  de- 
composes very  easily.  Potassium  chlorate,  which  is  so 
closely  related  to  it,  is  a  very  important  compound.  As 
we  have  already  seen,  it  gives  off  its  oxygen  under  the  in- 
fluence of  heat.  It  also  gives  up  oxygen  in  contact  with 
substances  which  have  the  power  to  take  it  up.  It  is  » 
powerful  oxidizing  agent. 

Potassium  hypoclilorite,  KC10,  formed  by  passing  chlo- 
rine into  a  dilute  solution  of  caustic  potash,  is  decomposed 
by  sulphuric  acid  thus: 

2KC10  +  H2S04  =  K2S04  +  2HC10. 

The  products  are  potassium  sulphate  and  hypoclilorous  acid. 
If  a  concentrated  solution  of  potassium  hypoclilorite  is  treat- 
ed with  sulphuric  acid,  the  hypochlorous  acid  formed  at 
once  undergoes  decomposition,  yielding  chlorine,  water, 
and  oxygen.  The  acid  itself  is  not  well  known.  The  prin- 
cipal compound  related  to  it  is  ' '  bleaching-powder,"  or  the 
substance  generally  known  as  "  chloride  of  lime,"  which  is 
familiar  to  every  one  on  account  of  its  application  as  a 
disinfecting  agent.  This  is  made  by  passing  chlorine  into 
slaked  lime,  which  from  a  chemical  standpoint  is  very 
similar  to  caustic  potash.  Just  as  when  chlorine  acts  on  a 
dilute  solution  of  caustic  potash  a  mixture  of  potassium 
chloride  and  potassium  hypoclilorite  is  formed,  so  when 


GULOltlNtS  ACIDS. 

chlorine  acts  on  slaked  lime  a  mixture  of  calcium  chloride, 
CaCl2,  and  calcium  hypochlorite,  Ca(OCl)2,  is  formed. 
This  mixture  is  bleaching-powder.  By  treating  it  with  an 
acid  it  gives  up  chlorine,  and  hence  it  affords  a  convenient 
way  of  transporting  chlorine.  Thousands  and  thousands 
of  tons  of  this  powder  are  manufactured.  The  chlorine  is 
passed  into  the  lime.  It  is  held  chemically  combined  until 
it  is  wanted,  when  it  can  be  liberated  by  adding  an  acid. 

EXPERIMENT  58. — Dissolve  40  grams  (or  about  1J  ounces) 
caustic  potash  in  100  cc.  water  in  a  beaker-glass,  and  pass 
chlorine  into  it.  When  chlorine  passes  freely  through  the 
solution,  thus  indicating  that  it  is  no  longer  absorbed,  stop 
the  action.  Filter  the  solution  and  allow  it  to  cool,  when 
crystals  of  potassium  chlorate  will  be  deposited,  mixed  with 
a  little  potassium  chloride.  Recrystallize  from  a  little  water. 
Filter  off  the  crystals  and  dry  them.  What  evidence  have 
you  that  the  substance  is  potassium  chlorate?  Does  it  give 
off  oxygen  when  heated  ?  In  a  dry  test-tube  pour  two  or 
three  drops  of  concentrated  sulphuric  acid  on  a  small  crys- 
tal of  the  substance.  Do  the  same  with  a  piece  of  potas- 
sium chlorate  from  the  laboratory  bottle.  Hold  the  mouth 
of  the  test-tube  away  from  the  face.  What  is  noticed  in 
each  case? — Evaporate  the  solution  from  which  the  crystals 
of  potassium  chlorate  have  been  removed.  On  allowing 
it  to  cool  crystals  will  again  be  deposited.  Take  them  out 
and  recrystallize  them.  Does  this  substance  give  off  oxy- 
gen when  heated?  Does  it  give  off  a  gas  when  treated 
with  sulphuric  acid?  Is  this  gas  colored?  Is  it  hydro- 
chloric acid?  How  do  you  know  that  it  is?  If  the  gas  is 
hydrochloric  acid,  what  is  the  solid  substance  from  which  it 
is  formed?  And  what  is  left  in  the  test-tube? 
8 


114 


INTRODUCTION  TO  CHEMISTRY. 


EXPERIMENT  59.— Mix  20  to  30  grams  (about  1  ounce) 
of  fresh  quick-lime  with  50  cc.  water.  After  the  slaking 
is  over,  pass  chlorine  into  it  until  the  gas  is  no  longer  ab- 
sorbed. Put  the  powder  thus  formed  in  a  flask  arranged 
as  shown  in  Fig.  28.  Pour  a  mixture  of  equal  parts  of 
sulphuric  acid  and  water  slowly  through  the  funnel-tube. 
Collect  by  displacement  of  air  the  gas  given  off.  What 


FIG.  28. 


evidence  have  you  that  the  gas  is  chlorine?  In  this  ex- 
periment the  substance  first  formed  is  bleaching-powder, 
or  "  chloride  of  lime."  This  is  decomposed  by  sulphuric 
acid,  yielding  chlorine.  The  formation  of  chlorine  is  sec- 
ondary, and  due  to  the  ease  with  which  hypochlorous  acid 
breaks  up  into  chlorine,  oxygen,  and  water.  The  tendency 
of  sulphuric  acid  to  extract  calcium,  just  as  it  does  potas- 
sium, and  to  put  hydrogen  in  its  place,  is  at  the  root  of 


BLEAC1IINQ-POWDER. 

the  matter.  Potassium  hypochlorite  and  potassium  chlo- 
ride, when  treated  with  sulphuric  acid,  yield  primarily  hy- 
pochlorous  acid  and  hydrochloric  acid: 

2KC10  +  H2S04  =  K2S04  +  2HC10; 
2KC1  +  H2S04  =  KaS04  +  2HC1. 

Thus  far  the  only  change  that  has  taken  place  is  the  ex- 
change of  hydrogen  for  potassium.  Now,  however,  the 
hypochlorous  acid  decomposes,  yielding  oxygen,  water,  and 
chlorine,  prohably  thus: 

2HC10  =  201  +  H20  +  0. 

The  oxygen  thus  liberated  would,  however,  act  upon 
hydrochloric  acid,  if  present,  and  set  chlorine  free  from  it: 

2HC1  +  0  =  H20  +  2CJ; 

«o  that,  if  a  mixture  of  potassium  hypochlorite  and  potas- 
sium chloride  be  treated  with  sulphuric  acid  we  would  ex- 
pect the  result  to  be  that  which  is  represented  in  this  equa- 
tion: 

KC10  +  KC1  +  H3S04  =  K2S04  +  H20  +  201. 

This  in  reality  expresses  what  takes  place,  as  has  been 
proved  experimentally.  The  decomposition  of  "  bleaching- 
powder "  takes  place  in  the  same  way,  the  only  difference 
being  that  in  one  case  we  have  to  deal  with  compounds  of 
the  metal  potassium,  while  in  the  other  we  have  to  deal 
with  analogous  compounds  of  the  metal  calcium. 

While  the  remaining  compounds  of  chlorine,  hydrogen, 
and  oxygen  cannot  be  considered  herein  detail,  a  reference 
to  the  series  as  a  whole  will  serve  to  call  to  mind  some  im- 
portant matters  of  general  interest.  There  are  four  of 


116  INTRODUCTION  TO  CHEMISTRY. 

these  compounds  which,  as  far  as  composition  is  concerned, 
bear  a  very  simple  relation  to  one  another.  They  are 
hypoclilorous  acid,  HC10;  chlorous  acid,  HC102;  chloric 
acid,  HC108;  and  perchloric  acid,  HC104.  Beginning  with 
hydrochloric  acid,  we  have  thus  a  series  of  compounds,  the 
successive  members  of  which  differ  by  one  combining  weight 
of  oxygen: 

Hydrochloric  acid HC1 

Hypochlorous  acid H010 

Chlorous  acid HC103 

Chloric  acid HC108 

Perchloric  acid HC104 

This  series  illustrates  very  clearly  the  law  of  multiple 
proportions  to  which  attention  has  already  been  called  (see 
ante,  p.  26).  [What  is  the  law  of  multiple  proportions  ? 
How  does  this  series  illustrate  the  law?] 

Compounds  of  Chlorine  and  Oxygen. — There  are  three 
of  these  compounds,  viz.:  chlorine  monoxide,  C1S0;  chlor- 
ine trioxide,  C1203;  and  chlorine  tetroxide,  C102  (or  C1204). 
They  are  unstable  substances  which  easily  break  up  into 
chlorine  and  oxygen.  They  are  not  easily  prepared  in  pure 
condition. 


CHAPTER  VI. 
ACIDS— BASES— NEUTRALIZATION—SALTS. 

We  cannot  work  in  a  laboratory  without  constant  refer- 
ence to  acids,  and  we  have  already  met  with  a  number  of 
substances  belonging  to  this  class.  It  is  now  time  for  us 
to  inquire  what  features  these  substances  have  in  common 
which  lead  chemists  to  call  them  all  acids.  What  is  there 
in  common  between  the  heavy,  oily  liquid,  sulphuric  acid, 
the  colorless  gas  hydrochloric  acid,  and  the  unstable  sub- 
stances chloric  and  hypochlorous  acids  ?  It  is  not  possible 
for  us  to  understand  the  nature  of  their  common  properties 
without  a  somewhat  premature  reference  to  a  class  of  sub- 
stances to  which  special  attention  will  be  called  in  due 
time.  These  are  the  alkalies,  which  are  the  most  marked 
representatives  of  the  class  of  substances  known  as  bases. 
These  two  classes,  the  acids  and  the  bases,  have  the  power  to 
destroy  the  characteristic  properties  of  each  other.  When  an 
acid  is  brought  in  contact  with  abase  in  proper  proportions, 
the  properties  of  both  the  acid  and  the  base  are  destroyed. 
They  are  said  to  neutralize  each  other.  This  act  of  neutral- 
ization is  an  extremely  important  one,  with  which  we  con- 
stantly have  to  deal  in  chemical  operations.  It  will  there- 
fore be  advisable  to  study  it  with  some  care. 

The  most  common  acids  are  sulphuric,  hydrochloric,  and 
nitric  acids.  Among  the  more  common  bases  are  caustic 


118  INTRODUCTION  TO  CHEMISTRY. 

soda,  caustic  potash,  and  lime.  Whenever  a  substance  with 
acid  properties  is  brought  together  with  a  substance  with 
basic  properties,  some  action  takes  place  which  causes 
the  destruction  of  the  acid  properties  and  the  basic  prop- 
erties. 

A  convenient  way  to  recognize  whether  a  substance  has 
acid  or  basic  properties  is  by  means  of  certain  color-changes. 
The  dye  litmus  is  blue.  If  a  solution  which  is  colored 
blue  with  litmus  be  treated  with  a  drop  or  two  of  an  acid, 
the  color  is  changed  to  red.  If  now  the  red  solution  be 
treated  with  a  few  drops  of  a  solution  of  a  base,  the  blue 
color  is  restored.  There  are  many  other  substances  which 
change  markedly  in  color,  according  to  whether  the  solu- 
tions in  which  they  are  present  have  acid  or  alkaline  prop- 
erties. An  infusion  of  red  cabbage,  for  example,  changes 
color  when  treated  with  an  acid,  and  recovers  its  color  when 
again  treated  with  an  alkali. 

EXPERIMENT  60.— Make  dilute  solutions  of  nitric,  hydro- 
chloric, and  sulphuric  acids  (1  part  dilute  acid,  such  as  is 
used  in  the  laboratory,  to  50  parts  water) ;  and  of  caustic 
soda  and  caustic  potash  (about  5  grams  to  100  cc.  of  water). 
Measure  off  about  20  cc.  of  each  of  the  acid  solutions. 
Add  a  few  drops  of  a  solution  of  blue  litmus.  Gradually 
add  to  each  of  the  measured  quantities  of  acid  sufficient 
dilute  caustic  soda  to  cause  the  red  color  just  to  change  to 
blue.  As  long  as  the  solution  is  red  it  is  acid.  When  it 
turns  blue  it  is  alkaline.  At  the  turning-point  it  is  neutral. 
The  operation  is  best  carried  on  by  means  of  a  burette, 
which  is  a  graduated  tube  with  an  opening  from  which 
small  quantities  can  be  poured.  A  convenient  shape  is 
that  represented  in  Fig.  20.  At  the  lower  end  is  a  small 
opening.  The  flow  of  the  liquid  from  the  burette  is  con- 


NEUTRALIZATION. 


119 


trolled  by  means  of  a  small  pinch-cock.  It  will  require 
some  practice  to  enable  the  student  to  know  exactly  when 
the  red  color  disappears  and  the  blue 
appears,  but  with  practice  the  point 
can  be  discerned  with  great  accuracy. 
Should  too  much  alkali  be  allowed  to 
get  into  the  acid,  add  a  small  measured 
quantity  of  the  acid  from  another 
burette.  Having  in  one  experiment  de- 
termined how  much  of  the  solution  of 
alkali  is  required  to  cause  the  red  color 
to  change  to  blue  in  operating  on  a 
given  quantity  of  the  acid  solution,  try 
the  experiment  again,  using  a  different 
quantity  of  the  acid  solution.  If  the  re- 
sults of  several  experiments  with  the 
same  acid  and  alkali  be  recorded  it  will 
be  found  that  there  is  a  definite  ratio  be- 
tween the  quantities  of  acid  and  alkali  so- 
lution required  to  neutralize  one  another. 
If,  for  example,  15  cc.  of  the  alkali  solution  are  required  to 
neutralize  20  cc.  of  the  acid  solution,  18  cc.  of  the  alkali  so- 
lution will  be  required  to  neutralize  24  cc.  of  the  acid  solu- 
tion, 30  cc.  to  neutralize  40  cc.,  etc.  In  other  words,  in 
order  to  neutralize  a  given  quantity  of  an  acid,  a  definite 
quantity  of  an  alkali  is  necessary.  Perform  similar  experi- 
ments with  the  other  acids.  Afterwards  carefully  examine 
the  numerical  results.  Suppose  it  should  require  15  cc.  of 
the  caustic-soda  solution  or  12  cc.  of  the  caustic-potash  so- 
lution to  neutralize  20  cc.  of  the  hydrochloric-acid  solution. 
Compare  the  quantities  of  these  alkali  solutions  necessary 
to  neutralize  equal  quantities  of  the  other  acids.  It  will 


FIG.  29. 


120  INTROUlTCTiqS  TO 

be  found  that,  if  it  requires  15  cc.  caustic-soda  solution  or 
12  cc.  caustic-potash  solution  to  neutralize  20  cc.  hydro- 
chloric-acid solution,  then  the  quantities  of  caustic-soda 
solution  and  caustic-potash  solution  required  to  neutralize 
any  definite  quantity  of  a  solution  of  another  acid  will  be 
to  each  other  as  15  to  12. 

It  appears,  therefore,  from  these  experiments  that  the  act 
of  neutralization  is  a 'definite  one,  which  takes  place  be- 
tween definite  quantities  of  acid  and  base.  The  next  ques- 
tion which  suggests  itself  is,  What  is  formed  when  the  acid 
and  base  are  neutralized?  To  determine  this  we  may  use  in 
larger  quantities  the  same  substances  as  those  used  in  the 
preceding  experiments. 

EXPERIMENT  61. — Dissolve  10  grams  caustic  soda  in  100 
cc.  water.  Add  hydrochloric  acid  slowly,  examining  the 
solution  from  time  to  time  by  means  of  a  piece  of  paper 
colored  blue  with  litmus.  As  long  as  the  solution  is  alka- 
line it  will  caijgg  no  change  in  the  color  of  the  paper.  The 
instant  it  passes  the  point  of  neutralization  it  changes  the 
color  of  the  paper  red;  when  exactly  neutral  it  will  neither 
change  the  blue  to  red,  nor,  if  the  color  be  changed  to  red 
by  means  of  another  acid,  will  it  change  it  back  again. 
When  this  point  is  reached,  evaporate  off  the  water  on  the 
water-bath  to  complete  dryness,  and  see  what  is  left.  Taste 
the  substance.  Has  it  an  acid  taste?  Does  it  suggest  any 
familiar  substance?  If  it  is  sodium  chloride,  how  ought  it 
to  conduct  itself  when  treated  with  sulphuric  acid?  Does 
it  conduct  itself  in  this  way?  Satisfactory  evidence  can  b|u 
given  that  the  substance  is  sodium  chloride.  It  is  not  an 
acid  nor  an  alkali.  It  is  neutral.  Its  formation  took 
place  according  to  the  equation 

HC1  +  NaOH  =  NaCl  +  HaO. 


ACIDS.  121 

Using  nitric  acid  and  caustic  soda,  the  product  formed 
is  sodium  nitrate.  Compare  it  with  sodium  nitrate  from 
the  laboratory  bottle.  Heat  a  small  specimen  of  each  in  a 
tube  closed  at  one  end.  What  do  you  observe?  Treat  a 
small  specimen  of  each  with  a  little  sulphuric  acid  in  test- 
tubes.  What  do  you  observe?  The  explanation  of  the 
changes  which  occur  in  these  cases  will  be  given  later. 
Here  we  are  principally  interested  to  kngw  that  the  sub- 
stance formed,  when  nitric  acid  acts  on  caustic  soda,  is  so- 
dium nitrate.  The  reaction  took  plaoe  thus: 

HN03  +  NaOH  =  NaNO,  +  H20. 

Similarly  sulphuric  acid  and  caustic  soda  gwe  sodium 
sulphate  and  water,  thus: 

H2S04  -f  2mOR  =  Na2S04  +  2H20. 
With  caustic  potash  similar   reactions  take  plap^  Hy- 


drochloric acid  and  caustic  potash  yield  potassium  chloride 
and  water  : 

HC1  +  KOH  =  KC1  +  H20. 

Nitric  acid  and  caustic  potash  yield  potassium  nitrate 
and  water: 

HN03  +  KOH  =  KN03  +  H,0. 

Sulphuric  acid  and  caustic  potash  yield  potassium  sul- 
phate and  water  : 

H2S04  +  2KOH  =  K2S04  +  2HaO. 

Considering  the  facts  just  learned,  we  see: 

(1)  That  an  acid  contains  hydrogen; 

(2)  That  a  base  contains  a  metal; 

(3)  That  when  an  acid  acts  on  a  base  the  hydrogen  and 
metal  exchange  places; 


122  INTRODUCTION  TO  CHEMISTRY. 

(4)  That  the  substance  obtained  from  the  acid  by  re> 
placing  the  hydrogen  by  a  metal  is  neutral; 

(5)  That  the   substance  formed  by  replacing  the  metal 
of  the  base  by  hydrogen  is  water. 

These  statements  are  of  general  application,  except  state- 
ment (4),  to  which  there  are  some  exceptions.  It  is  true  in 
some  cases  that  after  replacing  the  hydrogen  by  a  metal  the 
substance  has  an  alkaline  reaction;  and  in  other  cases  that 
the  product  has  an  acid  reaction. 

We  have  already  seen  that  hydrochloric  acid  and  sul- 
phuric acid  act  upon  certain  metals,  as  iron  and  zinc,  and 
that  the  action  consists  in  giving  up  hydrogen  and  taking 
up  metal  in  its  place.  The  products  of  this  action  are  the 
same  in  character  as  those  formed  by  the  action  of  acids 
on  bases. 

An  acid  is  a  substance  containing  hydrogen,  which  it 
easily  exchanges  for  a  metal  when  treated  with  a  metal 
itself,  or  with  a  compound  of  a  metal,  called  a  base. 

A  base  is  a  substance  containing  a  metal  combined  with 
hydrogen  and  oxygen.  It  easily  exchanges  its  metal  for 
hydrogen  when  treated  with  an  acid. 

The  products  of  the  action  of  an  acid  on  a  base  are,  first, 
water,  and,  second,  a  neutral  substance  called  asalt. 

In  the  example  already  given  sodium  chloride,  potassium 
chloride,  sodium  nitrate,  potassium  nitrate,  sodium  sul- 
phate, and  potassium  sulphate  are  salts. 

It  may  fairly  be  asked,  What  is  a  metal?  Unfortunately 
for  our  present  purpose,  it  is  by  no  means  an  easy  matter 
to  give  a  satisfactory  answer  to  this  question.  We  can  give 
examples  of  metals,  such  as  iron,  zinc,  silver,  calcium, 
magnesium,  etc. ;  but  when  we  attempt  to  discover  the  dis- 


NOMENCLATURE  OF  ACIDS. 

tinguishing  features  of  these  substances  we  are  somewhat 
at  a  loss  to  state  them.  In  general,  it  may  be  said 
that  to  the  chemist  any  element  is  a  metal  which  with 
hydrogen  and  oxygen  forms  a  product  which  has  the  power 
to  neutralize  acids;  that  is  to  say,  which  has  basic  properties. 
In  general,  any  element  which  has  the  power  to  enter  into 
an  acid  in  the  place  of  the  hydrogen  is  called  a  metal,  or  is 
said  to  have  metallic  properties.  This  is  the  sense  in 
which  the  word  metal  is  used  in  this  book. 

Nomenclature   of  Acids. — The  names  of  the    acids    of* 
chlorine  illustrate  some  of  the  principles  of  nomenclature  in 
use  in  chemistry.     That  acid  of  the  series  which  is  best, 
known  is  called  chloric  acid.     The  termination  ic  is  gener- 
ally used  in  naming  acids,  as  is  seen  in  the  names   hydro 
chloric,  sulphuric,  nitric,  etc.     If  a  second  acid  containing 
the  same  elements  exists  and  the  proportion  of  oxygen  con 
tained  in  it  is  smaller  than  in  the  acid  the  name  of   which 
ends  in  ic,  the  second  acid  is  given  a  name  ending  in   ous. 
Thus  chlorous  acid  contains  a  smaller  proportion  of  oxygen 
than  chloric  acid,  and  the  suffixes  ic  and  ous  signify  that 
fact.     We  have  many  other  examples  of  this  use  of  these 
suffixes  in  the  names  of  acids  as  well  as  in  the  names  of 
compounds  of  other  classes. 

In  the  series  of  chlorine  acids,  however,  this  simple  prin- 
ciple, which  is  sufficient  for  most  cases,  does  not  suffice.  In 
order,  therefore,  to  form  characteristic  names  for  the  other 
members  of  the  series  we  have  recourse  to  prefixes.  There., 
is  one  acid  which,  so  far  as  the  proportion  of  oxygen  con- 
tained in  it  is  concerned,  stands  below  chlorous  acid.  It  is 
called  fct/jp0chloroua  acid,  the  prefix  hypo  being  derived 
from  the  Greek  vno,  under.  Further,  there  is  an  acid  which 


124  INTRODUCTION  TO  CHEMISTRY. 

contains  a  larger  proportion  of  oxygen  than  chloric  acid. 
It  is  called  perchloric  acid,  the  Latin  prefix  per  signifying 
here  very  or  fully.  It  will  be  seen  that  the  names  of 
the  acids  vary  with  the  proportion  of  oxygen  contained  in 
them. 

Nomenclature  of  Bases. — As  pointed  out  above,  a  base  is 
a  compound  of  a  metal  with  hydrogen  and  oxygen.  Thus, 
caustic  soda  has  the  formula  NaOH,  caustic  potash  KOH, 
lime  Ca02H2,  etc.  They  are  commonly  known  as  hydrox- 
ides. In  order  to  distinguish  between  the  hydroxides  of  the 
different  metals,  the  names  of  the  metals  are  put  before  the 
name  hydroxide.  Thus,  caustic  soda,  NaOH,  is  called 
sodium  hydroxide;  caustic  potash,  KOH,  is  called  pofas- 
sium  hydroxide;  caustic  lime,  Ca02H2,  is  called  calcium 
hydroxide,  etc.  They  may  be  regarded  as  water  in  which 
a  part  of  the  hydrogen  has  been  replaced  by  a  metal,  and 
indeed  many  of  them  can  be  made  by  simply  bringing  the 
corresponding  metals  in  contact  with  water.  Thus,  as 
we  saw  in  experimenting  on  hydrogen,  when  sodium  or 
potassium  is  thrown  on  water  hydrogen  is  evolved.  The 
products  formed  were,  respectively,  sodium  hydroxide  and 
potassium  hydroxide.  These  compounds  are  called  hy- 
drates by  some  chemists,  the  name  implying  that  they  are 
derivatives  of  water.  The  name 'hydroxide  means  simply 
that  the  substances  contain  hydrogen  and  oxygen. 

Nomenclature  of  Salts. — Theoretically  every  metal  can 
yield  a  salt  with  every  acid.  The  salts  derived  from  a 
given  acid  receive  a  general  name,  and  'this  general  name 
is  qualified  in  each  case  by  the  name  of  the  metal  contained 
in  the  salt.  Thus  all  the  salts  derived  from  nitric  acid  are 
called  nitrates;  all  the  salts  derived  from  chloric  acid  are 
called  chlorates;  the  salts  of  sulphuric  acid  are  called  sul- 


NOMENCLATURE  OF  SALTS.  125 

phates.*  So  too,  further,  the  salts  of  chlorous  acid  are 
called  chlorites;  those  of  nitrous  acid,  nitrites;  those  of 
sulphurous  acid,  sulphites,  etc.,  etc.  It  will  be  noticed 
that  the  terminal  syllable  of  the  name  of  the  salt  differs 
according  to  the  name  of  the  acid.  If  the  name  of  the  acid 
ends  in  ic,  the  name  of  the  salt  derived  from  it  ends  in  ate. 
If  the  mime  of  the  acid  ends  in  ous,  the  name  of  the  salt 
ends  in  lie.  To  distinguish  between  the  different  salts  of 
the  same  acid,  the  name  of  the  metal  contained  in  it  is  pre- 
fixed. Thus,  the  potassium  salt  of  nitric  acid  is  called 
potassium  nitrate,  the  sodium  salt  is  called  sodium  nitrate; 
the  calcium  salt  of  sulphuric  acid  is  called  calcium  sulphate; 
the  magnesium  salt  of  nitrous  acid  is  magnesium  nitrite. 
The  calcium  salt  of  hypochlorous  acid  is  calcium  hypochlo- 
rite,  etc.,  etc.  [Give  the  name  and  formula  of  the  potas- 
sium salt  of  perchloric  acid. — Give  the  name  and  formula 
of  the  sodium  salt  of  hypochlorous  acid. — Give  the  name 
and  formula  of  the  sodium  salt  of  nitric  acid.] 

If  the  salts  of  hydrochloric  acid  were  named  in  accord- 
ance with  the  principle  just  explained,  they  would  be  called 
hydrochlor cites.  But  it  will  be  observed  that  these  salts 
are  identical  with  the  products  formed  by  direct  combina- 
tion of  the  metals  with  chlorine.  Thus,  hydrochloric  acid 
and  zinc  act  as  represented  in  the  equation: 

Zii  -f  2HC1  =  ZnCl,  +  2H, 
while  zinc  and  chlorine  act  thus: 

Zn  -f  201  =  ZnCla. 

*  If  the  principle  were  strictly  applied  the  salts  of  sulphuric  acid 
would  be  called  sulphurates,  but  for  the  sake  of  convenience  the 
name  is  shortened. 


126  INTRODUCTION  TO  CHEMISTRY. 

In  each  case  the  same  product,  ZtiCl2,  is  formed.  But 
these  compounds  of  metals  with  chlorine  are  called  chlorides 
as  has  already  been  explained.  Hence  the  name  hydro- 
chlorate  is  unnecessary. 

Acid  Properties  and  Oxygen. — The  observation  that  oxy- 
gen is  generally  present  in  acids  led  at  one  time  to  the  belief 
that  it  is  an  essential  constituent  of  these  substances. 
Hence  the  name  oxygen  was  given  to  it  (from'o*?;^,  acid, 
and  yrfrrctG),  I  form).  That  oxygen  is  not  essential  to  the 
existence  of  acid  properties  is  shown  in  the  case  of  hydro- 
chloric acid,  and  in  a  few  other  similar  cases.  It  must  be 
said,  however,  that  the  acid  properties  of  substances  are 
generally  due  to  the  presence  of  oxygen.  Some  substances 
with  basic  properties  can  be  converted  into  acids  by  causing 
them  to  combine  with  oxygen. 


CHAPTER  VII. 
NITROGEN.— AIR. 

WE  have  learned  that  when  substances  burn  in  the  air 
the  same  products  are  formed  as  when  they  burn  in  oxygen; 
and,  further,  that  there  is  something  besides  oxygen  present 
in  the  air  which  renders  the  burning  less  active  than  it  is 
in  oxygen  alone.  We  have  seen  (Experiment  24)  that  if  a 
I'iece  of  phosphorus  is  introduced  into  a  vessel  containing 
oxygen  the  gas  slowly  combines  with  the  phosphorus,  and 
phosphorus  pentoxide  is  formed,  which  dissolves  in  water. 
We  may  now  repeat  the  experiment,  using  air  instead  of 
oxygen. 

EXPERIMENT  62. — Arrange  the  apparatus  as  in  Fig.  4, 
Experiment  24.  Instead  of  a  plain  tube,  use  one  gradu- 
ated into  cubic  centimetres.  Enclose  60  to  80  cc.  air  in 
the  tube  over  water.  Arrange  the  tube  so  that  the  level  of 
the  water  inside  and  outside  is  the  same.  Note  the  tem- 
perature" of  the  air  and  the  height  of  the  barometer.  Re- 
duce the  observed  volume  to  standard  conditions.  Now 
introduce  a  piece  of  phosphorus,  as  in  Experiment  24,  and 
allow  it  to  stand  for  twenty-four  hours.  Draw  out  the 
phosphorus.  Again  arrange  the  tube  so  that  the  level  of 
the  water  inside  is  the  same  as  that  outside.  Make  the 
necessary  corrections  for  temperature  and  pressure.  It 
will  be  found  that  the  volume  has  diminished  considerably, 


128  INTRODUCTION  TO  CHEMISTRY. 

but  that  about  four  fifths  of  the  gas  originally  put  in  the 
tube  is  still  there.  If  the  work  is  done  carefully,  the  vol- 
ume of  the  gas  left  in  the  tube  will  be  to  the  total  volume 
used  as  79  to  100.  In  other  words,  of  every  100  cc.  air 
used  21  cc.  are  absorbed  by  phosphorus,  and  79  cc.  are  not. 
The  gas  absorbed  is  oxygen,  identical  with  the  oxygen 
made  from  the  oxide  of  mercury,  manganese  dioxide,  and 
potassium  chlorate.  The  gas  left  over  has  no  chemical 
properties  in  common  with  ox}7gen.  Carefully  take  the 
tube  out  of  the  vessel  of  water,  closing  the  mouth  with  the 
thumb  or  some  suitable  object  to  prevent  the  contents  from 
escaping.  Turn  it  with  the  mouth  upward,  and  introduce 
into  it  a  burning  stick.  It  is  extinguished.  This  residual 
gas  will  not  support  combustion,  and  cannot  therefore  be 
oxygen. 

The  experiment  just  performed  shows  us  that  the  air  is 
made  up  by  volume  of  21  per  cent  of  oxygen  and  79  per 
cent  of  a  gas  which  does  not  support  combustion.  This 
second  constituent  of  the  air  is  nitrogen. 

Preparation. — The  most  convenient  way  to  prepare  ni- 
trogen is  to  burn  a  piece  of  phosphorus  in  a  bell  jar  over 
water. 

EXPERIMENT  63.— Place  a  good-sized  stoppered  bell  jar 
over  water  in  a  pneumatic  trough.  In  the  middle  of  a  flat 
cork  about  three  inches  in  diameter  fasten  a  small  porce- 
lain crucible,  and  float  this  on  the  water  in  the  trough. 
Put  in  it  a  piece  of  phosphorus  about  twice  the  size  of  a 
pea,  and  set  fire  to  it.  Quickly  place  the  bell  jar  over  it.  At 
first  some  air  will  be  driven  out  of  the  jar.  [Why  ?]  The 
burning  will  continue  for  a  short  time,  and  then  gradually 
grow  less  and  less  active,  finally  stopping.  On  cooling,  it 
will  be  found  that  the  volume  of  gas  is  less  than  four  fifths 


COMPOSITION  OF  THE  AIR.  129 

the  original  volume,  for  the  reason  that  some  of  the  air  was 
driven  out  of  the  vessel  at  the  beginning  of  the  experiment. 
Before  removing  the  stopper  of  the  bell  jar  see  that  the 
level  of  the  liquid  outside  is  the  same  as  that  inside.  Try 
the  effect  of  introducing  successively  several  burning  bodies 
into  the  nitrogen, — as,  for  example,  a  candle,  a  piece  of  sul- 
phur, phosphorus,  etc. 

Ib  was  stated,  p.  53,  that  oxygen  is  used  up  in  the  breath- 
ing process.  If  this  is  so,  an  animal  should  die  if  placed 
in  an  enclosed  space  containing  a  limited  supply  of  oxygen. 

EXPERIMENT  64. — Place  a  live  mouse  in  a  trap  in  a  bell 
jar  over  water.  When  the  oxygen  is  used  up  the  mouse 
will  die.  After  the  animal  gives  plain  signs  of  discom- 
fort, it  may  be  revived  by  taking  away  the  bell  jar  and 
giving  it  a  free  supply  of  fresh  air. 

Anything  that  has  the  power  to  absorb  oxygen  may  be 
used  in  the  preparation  of  nitrogen  from  the  air.  To  avoid 
contamination  of  the  nitrogen  with  other  substances,  how- 
ever, it  is  necessary  to  use  something  which  does  not  form 
a  gaseous  product  when  burned.  Metallic  copper  is  con- 
venient, and  is  not  unfrequently  used.  It  is  only  necessary 
to  pass  air  over  heatetj  copper,  when  the  metal  combines 
with  oxygen,  forming  the  solid  copper  oxide,  CuO,  leaving 
the  nitrogen  uncombined.  The  nitrogen  and  oxygen  which 
make  up  the  air  are  not  chemically  combined  with  each 
other,  but  simply  mixed  together.  It  is  not  an  easy  mat- 
ter to  prove  this  statement  satisfactorily,  but  the  evidence 
is  so  strong  that  no  chemist  doubts  it. 

(1)  If  nitrogen  and  oxygen  are  mixed  together,  the 
mixture  conducts  itself  in  exactly  the  same  way  as  air. 
The  mixing  is  not  accompanied  by  any  phenomena  indi- 
cating chemical  action.  We  have  seen  that  the  union  of 
9 


130  INTRODUCTION  TO  CHEMISTRY. 

two  substances  is  accompanied  by  an  evolution  of  heat,  and 
that  whenever  a  chemical  act  takes  place  there  is  some 
change  in  the  temperature  of  the  substances.  When  ni- 
trogen and  oxygen  are  mixed  there  is  no  change  in  the  tem- 
perature of  the  gases. 

(2)  The  composition  of  a  chemical  compound  is  constant 
The  law  of  definite  proportions  is  founded  upon  a  very 
large  number  of  observations,  and  in  all  cases  in  which  we 
have    independent    evidence  that   chemical  action  takes 
place,  it  is  found  that  the  same  substances  combine  in  the 
same  proportions  to  form  the  same  product.     Variation  in 
the  composition  of  a  chemical  compound  is  not  known. 
The  composition  of  the  air  varies  slightly,  according  to  cir- 
cumstances, and  this  fact  may  be  regarded  as  evidence  that 
the  air  is  not  a  chemical  compound. 

(3)  Air  dissolves  somewhat  in  water.     If  air  which  has 
been  thus  dissolved  be  pumped  out  and  analyzed,  it  will  be 
found  to  have  a  composition  different  from  that  of  ordi- 
nary air.     Instead  of  containing  1  volume  of  oxygen  to  4 
volumes  of  nitrogen,  it  will  contain  1  volume  of  oxygen  to 
1.87  volumes  of   nitrogen.      The  relative  quantity  of  the 
oxygen  is  much  larger  in  air  which  has  been  dissolved  in 
water  than  it  is  in  ordinary  air.     This  is  due  to  the  fact 
that  oxygen  is  more  soluble  in  water  than  nitrogen  is.     In 
order,  however,  that  one  gas  may  dissolve  more  than  the 
other,  it  is  necessary  that  they  should  not  be  in  chemical 
combination.     If  they  were  in  chemical  combination  the 
compound  as  such  would  probably  dissolve. 

Occurrence  of  Nitrogen. — Besides  being  found  in  the  free 
state  in  the  air,  nitrogen  is  found  in  combination  in  a  large 
number  of  substances  in  nature.  It  is  found  in  the  nitrates, 
or  salts  of  nitric  acid,  particularly  as  the  potassium  salt. 


PROPERTIES  OF  NITROGEN.  131 

KN03,  known  as  saltpetre,  and  the  sodium  salt,  NaN03, 
known  as  Chili  saltpetre.  It  is  also  found  in  the  form  of 
ammonia,  which  is  a  compound  of  nitrogen  and  hydrogen, 
represented  by  the  formula  NH3.  Ammonia  occurs  in 
small  quantity  in  the  air,  and  is  formed  under  a  variety  of 
conditions,  to  which  reference  will  be  made,  when  the  sub- 
stance is  considered.  Nitrogen  occurs,  further,  in  most 
animal  substances  in  chemical  combination. 

Properties  of  Nitrogen. — We  have  seen  that  nitrogen  is 
a  colorless,  tasteless,  inodorous  gas.  It  does  not  support 
combustion,  nor  does  it  burn.  [Suppose  nitrogen  were 
combustible,  what  would  be  the  composition  of  the  atmos- 
phere?] Nitrogen  not  only  does  not  combine  with  oxygen 
readily,  but  it  does  not  combine  with  any  other  element 
except  at  very  high  temperature,  and  then  with  only  a 
few.  Just  as  it  does  not  support  combustion,  so  also  it 
does  not  support  respiration.  An  animal  would  die  in  it, 
not  on  account  of  any  active  poisonous  properties  possessed 
by  it,  but  for  lack  of  oxygen.  In  the  air  it  serves  the  use- 
ful purpose  of  diluting  the  oxygen.  If  the  air  consisted 
only  of  oxygen,  all  processes  of  combustion  would  certainly 
be  much  more  active  than  they  now  are.  What  the  effect 
on  animals  of  the  continued  breathing  of  oxygen  would  be, 
it  is  difficult  to  say. 

Other  Constituents  of  the  Air. — Besides  nitrogen  and 
oxygen  the  air  contains  other  substances,  some  of  which 
are  of  great  importance. 

EXPERIMENT  65. — Expose  a  few  pieces  of  calcium  chlo- 
ride on  a  watch-glass  to  the  air.  It  gradually  becomes 
liquid  by  absorbing  water  from  the  air.  See  Experiment 
42.  [What  is  a  salt  called  which  has  the  power  to  take  up 
water  from  the  air  and  dissolve  in  the  water  ?] 


132 


INTRODUCTION  TO  CHEMISTRY. 


EXPERIMENT  66. — Expose  some  clear  lime-water  to  the 
air.  It  soon  becomes  covered  with  a  white  crust.  A  simi- 
lar change  takes  place  if  baryta-water  be  exposed  in  the 
same  way.  Lime-water  is  made  by  putting  a  few  pieces  of 
quick-lime  in  a  bottle  and  pouring  water  upon  it.  The 
mixture  is  well  shaken  up  and  allowed  to  stand.  The  un- 
dissolved  substance  settles  to  the  bottom,  and  with  care  a 
clear  liquid  can  be  poured  off  the  top.  This  is  lime-water, 
which  is  a  solution  of  calcium  hydroxide,  Ca02Ha,  in 
water.  Baryta-water  is  a  solution  of  a  similar  compound 
of  the  metal  barium.  When  these  solutions  are  exposed 
to  nitrogen  or  oxygen,  or  to  an  artificially  prepared  mix- 
ture of  the  two  gases,  no  change  takes  place.  Further,  if 
air  is  first  passed  through  a  solution  of  caustic  soda  it  no 
longer  has  the  power  to  cause  the  formation  of  a  crust  on 
lime-water  or  baryta-water. 

EXPERIMENT  67. — Arrange  an  apparatus  as  shown  in 
Fig.  30.  The  wash-cylinders  A  and  B  are  half  filled  with 


FIG.  30. 


ordinary  caustic-soda  solution.     The  bottle  (7  is  filled  with 
water.     The  tube  D,  which  should  be  filled  with  water  and 


CONSTITVENTS  OF  Tim  AIR.  133 

provided  with  a  pinch-cock.,  acts  as  a  siphon.  Open  tlio 
pinch-cock  and  let  the  water  flow  slowly  out  of  the  bottle. 
As  it  flows  put  air  will  be  drawn  in  through  the  caustic-soda 
solution  in  the  wash-cylinders.  When  the  bottle  is  filled 
with  air  pour  some  water  in  again  so  that  it  is  about  a 
quarter  full.  Draw  this  water  off  as  before,  Now  remove 
the  stopper  from  the  bottle,  pour  in  20  to  30  cc.  lime- 
water  and  cork  the  bottle.  The  crust  formed  on  the  lime- 
water  will  now  be  hardly,  if  at  all,  perceptible.  There  is, 
therefore,  something  present  in  the  air  under  ordinary  cir- 
cumstances which  has  the  power  to  form  a  crust  on  lime- 
water  or  baryta-water,  and  which  can  be  removed  by  pass- 
ing the  air  through  caustic  soda.  Thorough  examination 
has  shown  that  this  is  the  compound  which  chemists  call 
carbon  dioxide  and  which  is  commonly  known  as  carbonic 
acid  gas.  It  is  the  substance  which  we  obtained  by  burn- 
ing charcoal  in  oxygen. 

EXPERIMENT  68. — Into  the  bottle  containing  the  air 
from  which  the  carbon  dioxide  has  be'en  removed  hold  a 
burning  stick  or  taper  for  a  moment.  Notice  whether  a 
crust  is  now  formed  on  the  lime-water.  Wood  and  the 
material  from  which  the  taper  is  made  contain  carbon. 
Explain  the  formation  of  the  crust  on  the  lime-water  after 
the  stick  of  wood  or  taper  has  burned  for  a  short  time  in 
the  vessel. 

EXPERIMENT  69. — Arrange  an  apparatus  as  shown  in  Fig. 
31.  The  bottle  A  contains  air.  B  contains  concentrated 
sulphuric  acid,  C  contains  granulated  calcium  chloride,  D 
is  carefully  dried  and  contains  a  few  pieces  of  granulated 
calcium  chloride  and  air.  Pour  water  through  the  funnel- 
tube  into  A,  the  air  will  be  forced  through  B  and  C  and  into 


134 


INTRODUCTION  TO  CHEMISTRY. 


D.  But  in  passing  through  B  and  G  the  moisture  contained 
in  it  will  be  removed,  and  the  air  which  enters  D  will  "be  dry. 
After  A  has  once  been  filled  with  water,  empty  it  and  fill  it 
again,  letting  the  dried  air  pass  into  D.  This  operation 
may  be  repeated  indefinitely.  The  calcium  chloride  in  D 
will  not  grow  moist. 

The  preceding  experiments  show  us  that  besides  oxygen 
and  nitrogen  there  are  present  in  the  air  water,  in  the 
form  of  vapor,  and  carbon  dioxide,  which  is  a  colorless  gas. 
Wherever  we  examine  the  air  these  two  substances  are 
found  to  be  present.  Indeed,  if  we  consider  the  circum- 


stances we  shall  see  that  they  must  be  present.  Evapora- 
tion is  taking  place  everywhere,  even  at  low  temperature, 
and  the  vapor  which  is  formed  is  carried  to  all  parts  of,  the 
earth  by  the  winds.  Whenever  any  of  our  ordinary  combus- 
tible substances  burn  in  the  air,  carbon  dioxide  is  formed, 
and,  further,  the  process  of  respiration  of  animals  also  gives 
rise  to  the  formation  of  carbon  dioxide,  which  is  given  off 
from  the  lungs. 


WATER  VAPOR  IN  THE  AIR.  135 

The  quantity  of  water  vapor  present  in  the  air  varies  be- 
tween comparatively  wide  limits.  At  any  given  tempera- 
ture the  air  cannot  hold  more  than  a  certain  quantity. 
When  it  contains  this  quantity  it  is  said  to  be  saturated. 
And  if  cooled  down  below  this  temperature  the  vapor 
partly  condenses  and  appears  now  as  water.  When  a  ves- 
sel containing  ice-water  is  placed  in  the  air,  that  which 
immediately  surrounds  the  vessel  is  cooled  down  below  the 
point  at  which  the  quantity  of  water  vapor  present  would 
saturate  the  air,  and  water  condenses  on  the  outside  of  tho 
vessel.  Every  one  has  noticed  that  on  a  warm  cloudy 
day  more  water  condenses  on  an  ice-pitcher  than  on  a  clear 
cool  day.  The  water  vapor  present  in  the  air  has  an  im- 
portant effect  on  man.  The  inhabitants  of  countries  with 
moist  climates  apparently  have  characteristics  which  are 
not  generally  met  with  in  those  who  inhabit  countries  with 
dry  climates.  The  difference  in  the  effects  of  moist  and  of 
dry  air  on  an  individual  is  well  known. 

Water  vapor  is  lighter  than  air;  hence  clouds  rise  and 
float  in  the  air.  When  air  which  is  charged  with  water 
vapor  comes  in  contact  with  cooler  air,  the  vapor  condenses 
and  falls  as  rain. 

The  quantity  of  water  vapor  in  a  given  volume  of  air 
can  be  determined  by  drawing  the  air  through  a  weighed 
tube  containing  calcium  chloride.  This  will  absorb  the 
water  and  increase  in  weight,  and  the  increase  in  weight 
will  represent  the  quantity  of  water  in  the  volume  of  air 
drawn  through  the  tube. 

The  quantity  of  carbon  dioxide  in  the  air  is  relatively 
very  small,  being  about  3  parts  in  10,000  parts  of  air.  It 
varies  slightly  according  to  the  locality  and  the  season.  It 
is  essential  to  the  growth  of  all  plants. 


136  INTRODUCTION  TO  CHEMISTRY. 

Besides  nitrogen  and  oxygen,  carbon  dioxide  and  water, 
the  air  contains  a  small  quantity  of  ammonia  (see  p.  138) 
and  a  large  number  of  other  substances  in  very  small 
quantities. 


CHAPTER  VIII. 

COMPOUNDS  OF  NITROGEN  WITH  HYDROGEN  AND 
OXYGEN. 

General  Conditions  which  Give  Rise  to  the  Formation  of 
the  Simpler  Compounds  of  Nitrogen. — We  have  seen  that 
nitrogen  is  an  inactive  element,  showing  little  tendency  to 
combine  with  other  elements.  It  is  nevertheless  an  easy 
matter  to  get  compounds  of  nitrogen  with  many  other  ele- 
ments, and  among  these  compounds,  some  of  those  which 
it  forms  with  hydrogen  and  oxygen  are  the  most  important. 

Whenever  a  compound  containing  carbon,  hydrogen,  and 
nitrogen  is  heated  in  a  closed  vessel,  so  that  the  air  does 
not  have  access  to  it  and  it  cannot  burn  up,  the  nitrogen 
passes  out  of  the  compound,  not  as  nitrogen,  but  in  com- 
bination with  hydrogen,  in  the  form  of  the  compound  called 
ammonia.  Nearly  all  animal  substances  contain  carbon, 
hydrogen,  oxygen,  and  nitrogen,  and  many  of  them  give 
off  ammonia  when  heated.  Similarly  compounds  contain- 
ing carbon,  oxygen,  and  hydrogen,  even  though  they  be 
thoroughly  dry,  when  heated,  give  off  oxygen  in  combina- 
tion with  hydrogen  in  the  form  of  water.  Some  animal 
substances  give  off  ammonia  when  they  undergo  decompo- 
sition in  the  air.  The  coal  which  is  used  for  making 


138  INTRODUCTION  TO  CHEMISTRY. 

illuminating  gas  contains  some  hydrogen  and  nitrogen  in 
chemical  combination,  and  when  the  coal  is  heated  ammo- 
nia is  given  off. 

When  animal  substances  undergo  decomposition  in  the 
presence  of  a  base  where  the  temperature  is  comparatively 
high,  the  nitrogen  combines  with  oxygen  and  the  metal 
of  the  base.  Either  a  nitrite  or  a  nitrate  is  formed;  that 
is  to  say,  either  a  salt  of  nitrous  acid,  HN02,  or  of  nitric 
acid,  HN03.  In  some  countries  where  the  conditions  are 
favorable  to  the  process,  immense  quantities  of  nitrates  are 
found,  chiefly  potassium  nitrate,  or  saltpetre,  KN03,  and 
sodium  nitrate,  or  Chili  saltpetre,  NaN03.  The  change  oj 
the  animal  substances  to  the  form  of  nitrates  is  probablj 
cailsed  by  myriads  of  minute  living  organisms.  How  they 
effect  the  change  is  not  known.  From  the  salts  of  nitric 
acid  which  are  found  in  nature,  nitric  acid  itself  can  easily 
be  extracted. 

Nearly  all  the  compounds  of  nitrogen  with  which  we  shall 
have  to  deal  are  made  either  from  ammonia  or  from  nitric 
acid. 

Ammonia,  NH3. — The  conditions  under  which  ammonia 
is  formed  have  been  mentioned.  The  chief  source  at  pres- 
ent is  the  "  ammoniacal  liquor"  of  the  gas-works.  This  is 
the  water  through  which  the  gas  has  been  passed  for  the 
purpose  of  removing  the  ammonia.  It  contains  ammonia 
in  solution.  By  adding  hydrochloric  acid  to  this  liquid, 
ammonium  chloride,  which  is  a  compound  of  the  acid  with 
ammonia,  is  formed.  This  is  the  well-known  substance 
sal  ammoniac.  This  name  was  first  applied  to  common 
salt  found  in  the  Libyan  desert  in  the  neighborhood  oj 
the  Temple  of  Jupiter  Ammon.  A  confusion  of  teraif 

afterwards  led  to  the  application  of  the  name  ammonium 
\ 


PREPARATION  OF  AMMONIA.  139 

chloride.  As  ammonium  chloride,  or  sal  ammoniac,  is 
the  most  common  compound  containing  ammonia,  it  is 
used  in  the  laboratory  for  making  ammonia.  For  this  pur- 
pose it  is  only  necessary  to  treat  the  salt  with  an  alkali. 

EXPEKIMENT  70.  —  To  a  little  ammonium  chloride  on  a 
watch-glass  add  a  few  drops  of  a  strong  solution  ^of  caustic 
soda,  and  notice  the  odor  of  the  gas  given  off.  Do  the  same 
thing  with  caustic  potash.  Mix  small  quantities  of  am- 
monium chloride  and  lime  in  a  mortar  and  notice  the  odor. 
The  odor  is  that  of  ammonia.  Has  the  ammonium  chloride 
this  odor  ? 

Preparation  of  Ammonia.  —  Ammonia  is  best  prepared 
by  mixing  quick-lime  and  ammonium  chloride  in  the  pro- 
portion of  2  parts  of  the  former  to  1  part  of  the  latter,  and 
gently  heating  the  mixture. 

It  has  been  shown  that  besides  the  ammonia,  which  is 
given  off  in  the  form  of  a  gas,  calcium  chloride,  CaCl2,  and 
water  are  formed  in  this  reaction.  It  is  represented  thus: 


CaO  =  2NH3  +  CaCl2  +  H20. 


This  curious  reaction  will  be  considered  more  fully  after  the 
nature  of  ammonia  has  been  studied. 

EXPERIMENT  71.  —  Arrange  an  apparatus  as  shown  in 
Figure  27,  p.  106.  In  the  flask  put  a  mixture  of  100  grams 
quick-lime  and  50  grams  ammonium  chloride.  Heat  on 
a  sand-bath.  After  the  air  is  driven  out,  the  gas  will  be 
completely  absorbed  by  the  water  in  the  first  Wolff's  flask. 
Disconnect  the  delivery-tube  from  the  series  of  Wolff's 
flasks,  and  connect  with  another  tube  bent  upward.  Col- 
lect some  of  the  escaping  gas  by  displacement  of  air,  plac- 
ing the  vessel  with  the  mouth  downward,  as  the  gas  is  much 


140  INTRODUCTION  TO  CHEMISTRY. 

lighter  than  air.  The  arrangement  is  shown  in  Fig.  32. 
The  vessel  in  which  the  gas  is  collected 
should  be  dry,  as  water  absorbs  ammonia 
very  readily.  Hence,  also,  it  cannot  be  col- 
lected over  water.  In  the  gas  collected  in- 
troduce a  burning  stick  or  taper.  Ammonia 
does  not  burn  in  air,  nor  does  it  support  com- 
bustion. In  working  with  the  gas  great  care 
must  be  taken  to  avoid  inhaling  it  in  any 
FIG.  32.  quantity.  After  enough  has  been  collected 
in  cylinders  to  exhibit  the  chief  properties,  connect  the 
delivery  tube  again  with  the  series  of  Wolff's  flasks,  and  pass 
the  gas  through  the  water  as  long  as  it  is  evolved. 

From  the  observations  made  in  the  experiments  just  per- 
formed, we  see  that  ammonia  is  a  colorless,  transparent 
gas.  It  has  a  very  penetrating  characteristic  odor.  In 
concentrated  form  it  causes  suffocation.  Its  specific  gravity 
is  0.586;  that  is  to  say,  it  is  but  little  more  than  half  as 
heavy  as  air.  It  can  easily  be  compressed  to  the  liquid 
form  by  pressure  and  cold.  When  the  pressure  is  removed 
from  the  liquefied  ammonia,  it  passes  back  to  the  form  of 
gas.  In  so  doing  it  absorbs  heat.  These  facts  are  taken 
advantage  of  for  the  artificial  preparation  of  ice.  Carre's 
ice-machine  is  used  for  this  purpose. 

Ammonia  does  not  burn  in  the  air,  but  does  burn  in 
oxygen.  It  is  absorbed  by  water  in  very  large  quantity. 
One  volume  of  water  at  the  ordinary  temperature  dissolves 
about  600  volumes  of  ammonia  gas,  and  at  0°  about  1000 
volumes. 

[PROBLEM. — A  litre  of  air  at  0°  weighing  1.293  grams,  and  the 
specific  gravity  of  ammonia  gas  being  0.586,  how  much  would  a 
litre  of  water  increase  in  weight  by  being  saturated  with  am- 
monia at  0°?] 


BASIC  PROPERTIES  OF  AMMONIA. 

The  solution  of  ammonia  in  water  is  what  we  commonly 
have  to  deal  with  under  the  name  of  ammonia.  It  is 
called  "Spirits  of  Hartshorn"  in  common  language.  The 
solution  has  the  odor  of  the  gas.  It  loses  all  its  gas  when 
heated  to  the  boiling  temperature.  The  solution  shows  a 
strong  alkaline  reaction  and  has  the  power  to  neutralize 
acids. 

EXPERIMENT  72. — Put  100  cc.  dilute  ammonia  solution  in 
an  evaporating-dish.  Try  its  effect  on  red  litmus  paper, 
Slowly  add  dilute  hydrochloric  acid  until  the  alkaline  re- 
action is  destroyed  and  the  solution  is  neutral.  Evaporate 
to  dryness  on  a  wafer-bath.  Compare  the  substance  thus 
obtained  with  sal- ammoniac,  or  ammonium  chloride.  Taste 
them.  Heat  them  on  a  piece  of  platinum  foil.  Treat  them 
with  a  caustic  alkali.  Treat  with  a  little  concentrated  sul- 
phuric acid  in  dry  test-tubes.  Do  they  appear  to  be  iden- 
tical ?  The  product  is  ammonium  chloride,  NH4C1. 
Similarly  sulphuric  acid  and  ammonia  yield  ammonium 
sulphate ;  nitric  acid  and  ammonia  yield  ammonium  ni- 
trate, etc. 

EXPEEIMENT  73. — Fill  a  cylinder  with  ammonia  gas,  and 
another  of  the  same  size  with  hydrochloric-acid  gas.  Bring 
them  together  with  their  mouths  covered.  Quickly  remove 
the  covers,  when  a  dense  white  cloud  will  appear  in  and 
about  the  cylinders.  This  will  soon  settle  on  the  walls  of 
the  vessels  as  a  light  white  solid.  It  is  ammonium  chloride. 
Thus,  from  two  colorless  gases  we  get  a  solid  substance  by 
an  act  of  chemical  combination.  Heat  is  evolved  in  the 
act  of  combination. 

We  have  seen  that  the  alkalies  are  strong  bases,  and  that 
bases  are  compounds  of  metals  with  hydrogen  and  oxygen. 
Certainly  those  substances  which  show  an  alkaline  reaction 


142  INTRODUCTION  TO  CHEMISTRY. 

are  compounds  of  metals  with  hydrogen  and  oxygen.  But 
in  the  solution  of  ammonia  in  water  we  have  a  substance 
which  shows  an  alkaline  reaction  and  which  acts  in  nearly 
all  respects  very  much  like  a  solution  of  sodium  hydroxide 
or  potassium  hydroxide.  The  salts  which  ammonia  forms 
with  acids  are  very  similar  to  sodium  and  potassium  salts. 
What  is  the  substance  which  has  the  alkaline  reaction? 
and  what  are  the  salts  which  are  formed  by  the  action  of 
"acid  on  ammonia?  In  the  first  place,,  it  has  been  found 
that  when  an  acid  acts  on  ammonia  the  two  combine  di- 
rectly without  the  formation  of  anything  but  the  salt. 
Thus  ammonia  and  hydrochloric  acid  form  ammonium 
chloride  : 

NH3  +  HC1  =  NH4C1. 

Ammonia  and  nitric  acid  form  ammonium  nitrate  : 
NH3  +  HN03  =  NH4N03,  etc.,  etc. 

On  comparing  the  formulas  of  ammonium  salts  with 
those  of  potassium  and  sodium  salts  we  see  that,  while  in 
the  potassium  and  sodium  salts  the  metals  potassium  and 
sodium  take  the  place  of  the  hydrogen  of  the  acids,  in  the 
ammonium  salts  the  place  of  the  acid  hydrogen  appears  to 
be  taken  by  a  compound  of  the  formula  NH4.  It  has  been 
suggested,  and  the  idea  has  been  generally  accepted,  that 
when  ammonia  gas  dissolves  in  water  an  unstable  compound 
of  the  formula  NHOH  is  formed  thus  : 


H20  =  NH4OH. 

In  this  hydroxide,  as  in  the  salts  of  ammonia,  the  com- 
pound NH4  appears  to  play  the  part  of  a  metal.     The  com- 


AMMONIUM  SALTS.  143 

pound  NH4  is,  however,  wholly  hypothetical.  As  it  appears 
to  be  this  which  plays  the  part  of  a  metal  in  the  solution  as 
well  as  in  the  salts,  the  name  ammonium  has  been  given  to 
it,  the  ending  ium  being  that  which  is  usually  given  to 
signify  metallic  character.  We  speak,  then,  of  ammonium 
salts,  just  as  we  speak  of  potassium  or  sodium  or  calcium 
salts.  In  the  ammonium  salts  the  hypothetical  compound 
metal  ammonium,  NH4,  is  assumed  to  be  present.  If,  how- 
ever, we  attempt  to  set  it  free  or  to  set  its  hydroxide  free, 
we  get  ammonia.  On  treating  ammonium  chloride  with 
lime,  if  any  action  takes  place  at  all  we  would  expect  it  to 
be  that  represented  by  the  equation 

2NH4C1  +  CaO  =  CaCl2  +  (NHJ  ,0; 

that  is  to  say,  we  would  expect  the  calcium  and  ammo- 
nium and  the  oxygen  and  the  chlorine  to  exchange  places. 
Perhaps  this  is  the  action  which  takes  place  at  first.  But 
the  compound  (NH4)20,  or  ammonium  oxide,  if  formed  at 
all,  breaks  up  at  once  into  ammonia  and  water,  thus  : 


So,  too,  if  ammonium  hydroxide,  NH4OH,  is  present  in 
the  solution  of  ammonia  in  water,  it  breaks  up  very  readily 
into  ammonia  and  water  under  the  influence  of  gentle 
heat  : 

NHOH  =  NH       H0. 


Composition  of  Ammonia.  —  By  oxidation  under  the  proper 
conditions  it  is  possible  to  convert  the  hydrogen  of  am- 
monia into  water  and  leave  the  nitrogen  in  the  free  state. 


144  INTRODUCTION  TO  CHEMISTRY. 

As  water  and  nitrogen  are  the  only  products  formed,  and 
the  quantity  of  oxygen  used  up  in  the  oxidation  is  equal  to 
the  quantity  of  oxygen  found  in  the  water  formed,  it  fol- 
lows that  nitrogen  and  hydrogen  are  the  only  elements  con- 
tained in  ammonia. 

When  electric  sparks  are  passed  for  some  time  through 
a  mixture  of  nitrogen  and  hydrogen,  some  ammonia  is 
formed.  Conversely,  when  electric  sparks  are  passed  for  a 
time  through  ammonia,  nitrogen  and  hydrogen  are  ob- 
tained. 

If,  in  the  oxidation  of  a  known  quantity  of  ammonia,  the 
water  formed  and  the  nitrogen  left  uncombined  be  accu- 
rately determined,  it  will  be  found  that  in  ammonia  the  ele- 
ments are  combined  in  the  proportion  of  fourteen  parts  ~by 
weight  of  nitrogen  to  three  parts  ~by  weight  of  hydrogen. 
This  fact  is  expressed  by  the  formula  NH3;  14  being  the 
combining  weight  of  nitrogen. 

The  proportion  by  volume  in  which  the  two  elements 
combine  may  be  determined  by  the  following  method. 
When  ammonia  is  treated  with  chlorine  it  is  decomposed, 
the  great  affinity  of  hydrogen  for  chlorine  causing  them  to 
unite.  The  nitrogen  is  left  uncombined.  The  reaction  is 
represented  thus : 

NH3  +  301  =  N  +  3HC1. 

Hydrogen  and  chlorine  unite  in  equal  volumes,  as  we 
have  already  learned.  Now,  if  we  start  with  a  measured 
volume  of  chlorine  and  add  ammonia  to  it  until  it  is  all 
used  up,  we  know  that  the  volume  of  hydrogen  which  has 
been  extracted  from  ammonia  is  equal  to  the  volume  of 
chlorine  with  which  we  started.  If  we  measure  the  nitrogen 


VOLUMES  OF  COMBINING   OASES. 


145 


left  over,  we  know  what  volume  of  nitrogen  was  combined 
with  the  volume  of  hydrogen  already  determined.  We 
would  find  that  the  volume  of  nitrogen  to  that  of  the  hy- 
drogen with  which  it  was  combined  is  as  1  to  3;  or  in  am- 
monia 1  volume  of  nitrogen  is  combined  with  3  volumes  of 
hydrogen. 

When  a  given  volume  of  ammonia  is  decomposed  into 
nitrogen  and  hydrogen,  the  mixture  occupies  just  twice  the 
volume  that  the  ammonia  did;  or,  if  a  mixture  of  nitrogen 
and  hydrogen  in  the  proper  proportions  to  form  ammonia 
be  caused  to  combine,  the  ammonia  formed  would  occupy 
one  half  the  volume  occupied  by  the  mixture  of  gases. 

Relations  between  the  Volumes  of  Combining  Gases. — In 
studying  the  volume  relations  of  hydrogen,  chlorine,  and 
hydrochloric  acid  with  reference  to  one  another,  we  found 
that  when  hydrogen  and  chlorine  combine  one  volume  of 
the  one  combines  with  one  volume  of  the  other,  and  two 
volumes  of  the  product  are  formed.  These  facts  may  be 
represented  graphically  thus: 


and         combine  to  form 


2  volumes  hydro- 
chloric acid. 


When  hydrogen  and  oxygen  combine,  two  volumes  of 
hydrogen  combine  with  one  volume  of  oxygen;   and  the 
three  volumes  of  gas  thus  combined  form  two  volumes  of 
water  vapor: 
10 


146  INTRODUCTION  TO  CHEMISTRY. 

2  volumes  hydrogen 


and      combine  to  form 


2  volumes 
water  vapor. 


Finally,  we  have  just  learned  that  one  volume  of  nitrogen 
combines  with  three  volumes  of  hydrogen  to  form  two  vol- 
umes of  ammonia: 

3  volumes  hydrogen 


and 


combine  to  form 


2  volumes 
ammonia. 


A  careful  study  of  the  volumes  of  combining  gases  has 
shown  that  these  volumes  always  bear  a  simple  relation  to 
one  another  and  to  the  volumes  of  the  products  formed. 
The  three  cases  already  considered  represent  the  more 
common  relations  met  with  among  the  elements. 

It  is  clear  that  the  three  elements  chlorine,  oxygen,  and 
nitrogen  influence  hydrogen  differently.  One  volume  of 
chlorine  can  hold  in  combination  but  one  volume  of  hydro- 
gen. One  volume  of  oxygen  can  hold  in  combination  two 
volumes  of  hydrogen,  and  at  the  same  time  cause  a  conden- 


SPECIFIC  GRAVITY  OF  OASES.  147 

sation  of  volume  from  three  volumes  of  gas  to  two.  One 
volume  of  nitrogen  can  hold  in  combination  three  volumes 
of  hydrogen,  and,  at  the  same  time,  cause  the  condensation 
of  four  volumes  of  gas  to  two. 

Relations  between  the  Specific  Gravities  of  Gases  and 
their  Combining  Weights. — Attention  has  already  been 
called  to  the  fact  that  the  weights  of  equal  volumes  of 
hydrogen,  chlorine,  and  oxygen  stand  in  the  same  relation 
to  one  another  as  the  combining  weights.  Nitrogen  is  no 
exception  to  this  rule,  The  specific  gravity  of  nitrogen  is 
0.967.  One  litre  of  nitrogen  weighs  1.2553  grams.  The 
specific  gravity  of  hydrogen  is  0.0693;  and  the  weight  of  a 
litre  of  hydrogen  is  0.089578.  But  0.0693  :  0.967  :  :  1  : 14 
and,  of  course,  0.089578  : 1.2553  :  :  1  : 14.  The  accepted 
combining  weight  of  nitrogen  is  14. 

These  remarkable  facts  may  be  represented  graphically 
thus: 


i 

itre  of  hydrogen       : 
eighs  0.089578  gr. 

litre  of  chlorine       1  litre  of  oxygen     1  litre  of  nitrog< 
weighs  3.17  gr.           weighs  1.429  gr.       weighs  1.2553  g 

These  figures  bear  to  one  another  the  relations  expressed 
by  the  figures  1,  35.4,  16,  and  14.  But  these  last  figures 
very  nearly  express  the  combining  weights  of  the  ele- 
ments. It  appears,  therefore,  that  the  combining  weights 
of  some  of  the  gaseous  elements  bear  to  one  another  the  same 
relations  as  the  weights  of  equal  volumes  of  the  gases. 

Observations  of  this  kind,  together  with  other  observa- 
tions on  the  conduct  of  gases,  have  led  to  a  very  important 
conception  in  regard  to  the  nature  of  gases  and  the  constitu- 
tion of  matter.  This  will  be  considered  further  on.  For  the 


148  INTRODUCTION  TO  CHEMISTRY. 

present  it  will  be  best  to  confine  our  attention  to  the  facts, 
so  that  when  we  begin  to  speculate  in  regard  to  the  hidden 
causes  of  the  phenomena  observed  we  shall  have  some 
foundation  for  our  speculations  to  rest  upon. 

Nitric  Acid,  HN03. — To  effect  the  direct  union  of  nitro- 
gen with  oxygen  and  hydrogen  is  not  easier  than  to  effect 
the  direct  union  of  nitrogen  with  hydrogen  to  form  ammo- 
nia. Nevertheless,  the  silent  and  continuous  action  of 
minute  organisms  in  the  soil  is  always  tending  to  trans- 
form the  waste  products  of  animal  life  into  compounds 
closely  allied  to  nitric  acid.  The  process  of  nitrification  has 
already  been  referred  to.  It  is  plainly  an  oxidizing  pro- 
cess. In  general,  by  oxidation  the  nitrogen  of  animal  sub- 
stances is  converted  into  nitric  acid,  while  by  reduction  it 
is  converted  into  ammonia. 

Preparation  of  Nitric  Acid. — In  preparing  nitric  acid  we 
always  start  with  a  nitrate,  and  replace  the  metal  by  hydro- 
gen. This  is  done  in  the  same  way  that  the  metal  sodium 
in  sodium  chloride  is  replaced  by  hydrogen  in  the  prepara- 
tion of  hydrochloric  acid, — viz.,  by  treating  the  salt  with  a 
strong  acid. 

SNaCl  +  H2S04  =  Na2S04  +  2HC1; 
2NaN03  +  H2S04  =  Na2SO4  +  2HNO,. 

The  action  is  due  to  the  difference  between  the  strengths 
of  the  two  acids,  sulphuric  and  nitric  acids.  We  call 
one  acid  stronger  than  another  when  the  former  decom- 
poses the  salts  of  the  latter,  appropriating  the  metal  and 
setting  the  weaker  acid  free.  In  this  sense  sulphuric  acid 
is  a  strong  acid,  stronger  than  either  hydrochloric  or  nitric 
acid.  The  designation  is  not  an  accurate  one,  for  the  rela- 
tive strengths  of  the  acids  vary  somewhat  with  surrounding 


NITRIC  ACID. 


149 


conditions,  so  that  an  acid  may  be  strong  under  some  cir- 
cumstances and  comparatively  weak  under  others.  For 
most  cases  which  we  shall  have  to  deal  with  in  this  stage  of 
our  study  the  expression  is  satisfactory,  and  it  will  facili- 
tate our  study  to  recognize  the  fact  that  a  strong  acid  de- 
composes the  salt  of  a  weak  acid,  setting  the  latter  free. 

EXPERIMENT  74.—  Arrange  an  apparatus  as  shown  in 
Fig.  33.     In  the  retort  put  25  grams  sodium  nitrate  (Chili 


FIG.  33. 

saltpetre)  and  15  grams  concentrated  sulphuric  acid.  On 
gently  heating,  nitric  acid  will  distil  over,  and  be  condensed 
in  the  receiver.  After  the  acid  is  all  distilled  off,  remove 
the  contents  of  the  retort.  Recrystallize  the  substance 
from  water,  and  compare  it  with  the  sodium  sulphate  ob- 
tained in  the  preparation  of  hydrochloric  acid.  (See  Ex- 
periment 57.)  In  the  latter  stage  of  the  operation  the  ves- 
sels become  filled  with  a  reddish-brown  gas.  The  acid 
which  is  collected  has  a  somewhat  yellowish  color. 
Pure  nitric  acid  is  a  colorless  liquid.  It  gives  off  color- 


150  INTRODUCTION  TO  CHEMISTRY. 

less  fumes  when  exposed  to  the  air.  When  boiled  it  un- 
dergoes slight  decomposition  into  oxygen,  water,  and  com- 
pounds of  nitrogen  and  oxygen.  One  of  these  compounds 
is  colored,  and  it  is  this  which  is  noticed  in  the  above  ex- 
periment, and  whenever  strong  nitric  is  boiled.  Nitric  acid 
undergoes  a  similar  decomposition  when  exposed  to  the  ac- 
tion of  the  direct  rays  of  the  sun.  In  consequence  of  this 
decomposition  bottles  containing  strong  nitric  acid  always 
contain  a  reddish-brown  gas  above  the  liquid  after  standing 
for  some  time.  It  acts  violently  on  a  great  many  sub- 
stances, disintegrating  them.  It  causes  bad  wounds  in  con- 
tact with  the  flesh ;  eats  through  clothing;  burns  wood; 
dissolves  metals;  and  is  altogether  one  of  the  most  active 
of  chemical  substances.  In  working  with  the  concentrated 
acid  it  is  necessary  to  exercise  the  greatest  care. 

Commercial  nitric  acid  contains  only  about  68  per  cent 
of  the  chemical  compound  HN03.  The  rest  is  mostly  wa- 
ter, though  there  are  several  impurities  in  small  quantity. 
In  order  to  get  concentrated  pure  acid  from  this  it  must  be 
distilled  after  the  addition  of  some  concentrated  sulphuric 
acid. 

EXPERIMENT  75. — Mix  together  400  grams  concentrated 
sulphuric  acid  and  80  grams  ordinary  concentrated  nitric 
acid.  Pour  the  sulphuric  acid  into  the  nitric  acid.  Distil 
the  mixture  from  a  retort  arranged  as  in  Experiment  74, 
taking  care  to  keep  the  neck  of  the  retort  cool  by  placing 
filter-paper  moistened  with  cold  water  on  it.  Use  the 
acid  thus  obtained  for  the  purpose  of  studying  the  proper- 
ties of  pure  nitric  acid. 

In  consequence  of  the  ease  with  which  nitric  acid  decom- 
poses, giving  up  oxygen,  it  is  an  excellent  oxidizing  agent, 
and  is  much  used  in  the  laboratory  in  this  capacity.  To 


NITRIC  ACID. 

illustrate  its  oxidizing  power,  the  following  experiments 
may  be  performed  : 

EXPERIMENT  76. — Pour  concentrated  nitric  acid  into  a 
wide  test-tube,  so  that  it  is  about  one  fourth  filled.  Heat 
the  end  of  a  stick  of  charcoal  of  proper  size,  and,  holding 
the  other  end  with  a  forceps,  introduce  the  heated  end  into 
the  acid.  It  will  continue  to  burn  with  a  bright  light,  even 
though  it  be  placed  below  the  surface  of  the  liquid.  The 
action  is  oxidation.  The  charcoal  in  this  case  finds  the 


FIG.  34. 


oxygen  in  the  acid,  and  not  in  the  air.  Great  care  must 
be  taken  in  performing  this  experiment.  The  charcoal 
should  not  come  in  contact  with  the  sides  of  the  test-tube. 
A  large  beaker  glass  should  be  placed  beneath  the  test-tube, 
so  that,  in  case  it  should  break,  the  acid  would  be  caught 
and  prevented  from  doing  harm.  The  arrangement  of  the 
apparatus  is  shown  in  Fig.  34. 

The  gases  given  off  from  the  tube  are  offensive  and  poi- 
sonous.    Hence  this  as  well  as  all  other  experiments  with 


152  INTRODUCTION  TO  CHEMISTRY. 

nitric  acid  should  be  carried  on  under  a  hood  in  which  the 
draught  is  good. 

EXPEKIMENT  77.  —  Boil  a  little  strong  nitric  acid  in  a 
test-tube  in  the  upper  part  of  which  some  horse-hair  has 
been  introduced  in  the  form  of  a  stopper.  The  horse-hair 
will  take  fire  and  burn,  and  leave  a  white  residue.  Hold 
the  test-tube  with  a  forceps  over  a  vessel  to  catch  the  con- 
tents should  the  tube  break. 

EXPERIMENT  78.  —  In  a  small  flask  put  a  few  pieces  of 
granulated  tin.  Pour  on  this  just  enough  strong  nitric 
acid  to  cover  it.  Heat  gently  over  a  small  flame.  Soon 
action  will  take  place.  Colored  gases  will  be  evolved,  the 
tin  will  disappear,  and  in  its  place  will  be  found  a  white 
powder.  This  consists  mostly  of  tin  and  oxygen.  (See 
Experiment  15.) 

The  experiments  just  performed  illustrate  the  oxidizing 
power  of  nitric  acid.  Like  other  acids,  nitric  acid  forms  salts 
with  the  metals.  These  may  be  made  by  treating  the  metals 
themselves  with  the  acid,  but  in  this  case  the  formation 
of  the  salt  is  accompanied  by  another  kind  of  action  which 
is  quite  characteristic  of  nitric  acid.  When  nitric  acid  acts 
on  most  metals  hydrogen  is  first  displaced  by  the  metal,  and 
nitrates  are  formed,  as  we  would  expect.  Thus,  if  M  repre- 
sents a  metal,  and  it  be  brought  into  nitric  acid,  we  should 
expect  the  reaction  to  take  place  as  represented  in  the 
equation 


But  as  nitric  acid  gives  np  oxygen  readily,  it  appears  that 
the  displaced  hydrogen  combines  with  oxygen  from  the 
acid  reducing  it,  and  causing  the  formation  of  compounds 
of  oxygen  and  nitrogen  containing  a  smaller  proportion  of 


NITRIC  ACID.  153 

oxygen  than  the  acid.  Thus,  one  product  of  the  action  is 
the  compound  N02,  called  nitrogen  peroxide.  Its  forma- 
tion may  be  represented  thus  : 

HN08  +  H  =  H20  +  N03. 

Another  compound  which  is  frequently  formed  is  nitric 
oxide,  NO.     Its  formation  may  be  represented  thus  : 

HN03  +  3H  =  2H20  +  NO. 

The  reduction  may  be  carried  still  farther,  yielding  ni- 
trous oxide,  N20  : 

2HN03  +  8H  =  5H20  +  N20. 

Under  other  circumstances  the  reduction  may  be  carried 
still  farther,  the  last  product  of  the  action  being  ammonia, 


As  nitrogen  peroxide  is  a  colored  gas  and  some  of  it  is 
always  formed  when  nitric  acid  acts  on  metals  in  the  air,  the 
presence  of  the  reddish-brown  substance  observed  in  the 
experiments  already  performed  with  nitric  acid  will  be 
readily  understood. 

EXPERIMENT  79.  —  Dissolve  a  few  pieces  of  copper  foil 
in  ordinary  commercial  nitric  acid  diluted  with  about  half 
its  volume  of  water.  The  operation  should  be  carried  on 
in  a  good  sized  flask  and  under  an  efficient  hood.  When 
the  copper  has  disappeared,  pour  the  blue  solution  into  an 
evapora  ting-dish,  and  evaporate  down  to  crystallization, 
Compare  the  substance,  thus  obtained  with  copper  nitrate. 
—Heat  specimens  of  each.  —  Treat  small  specimens  with  sul- 
phuric acid.  —  Do  the  two  substances  appear  to  be  iden- 
tical ? 

EXPERIMENT  80.  —  Heat  specimens  of  potassium  nitrate, 


154  INTRODUCTION  TO  CHEMISTRY. 

sodium  nitrate,  lead  nitrate,  and  any  other  nitrates  which 
may  be  available.  All  are  decomposed  giving  off  oxygen,  in 
some  cases  mixed  with  oxides  of  nitrogen,  among  which  is 
nitrogen  peroxide,  which  may  be  recognized  by  its  color. 
A II  salts  of  nitric  acid  are  decomposed  ~by  heat,  and  all  are 
soluble  in  water. 

EXPEEIMENT  81. — Try  the  solubility  in  water  of  the 
nitrates  used  in  the  last  experiment. 

The  formation  of  ammonia  by  reduction  of  nitric  acid 
may  be  shown  by  the  following  experiment. 

EXPERIMENT  82. — In  a  good-sized  test-tube  treat  a  few 
pieces  of  granulated  zinc  with  dilute  sulphuric  acid.  What 
is  evolved  ?  Prove  it.  Now  add  drop  by  drop  dilute 
nitric  acid.  The  hydrogen  ceases  to  be  given  off.  Pour 
the  contents  of  the  tube  into  an  evaporating-dish  and 
evaporate  the  liquid.  Put  the  residue  into  a  test-tube  and 
add  caustic-soda  solution,  when  the  smell  of  ammonia  will 
be  noticed.  Try  the  action  of  the  gas  on  red  litmus  paper. 
Moisten  the  end  of  a  glass  rod  with  a  little  hydrochloric 
acid  and  hold  it  in  the  tube.  White  fumes  are  seen. 
What  are  they  ?  Do  the  same  with  nitric  acid.  What  are 
the  fumes  in  this  case  ? 

Aqua  regia  is  made  by  mixing  together  concentrated 
nitric  and  hydrochloric  acids.  It  is  an  excellent  solvent. 

Nitrous  Acid,  HN02. — Among  the  reduction  products 
of  nitric  acid  is  nitrous  acid,  HN02.  This  acid  is  most 
easily  prepared  in  the  form  of  a  salt  by  reducing  a  nitrate. 
Thus,  if  potassium  nitrate,  KN03,  be  melted  together  with 
metallic  lead,  the  lead  extracts  a  part  of  the  oxygen  aid 
leaves  potassium  nitrite,  KN02. 

KN09  +  Pb  =  KNOa  +  PbO. 


ACID. 

EXPERIMENT  83.—  Heat  together  in  a  shallow  iron  plate 
25  grams  potassium  nitrate  and  about  50  grains  metallic 
lead.  When  both  are  melted  stir  them  together  as  thoroughly 
as  possible.  After  the  mass  is  cooled  down,  break  it  up  and 
treat  with  water  in  a  flask.  The  potassium  nitrite  will 
dissolve,  while  the  lead  oxide  and  unused  lead  will  not  dis- 
solve. Filter  off.  Add  a  little  sulphuric  acid  to  some  of 
the  solution.  A  colored  gas  will  be  given  off.  See  whether 
a  solution  of  potassium  nitrate  acts  in  the  same  way. 

Nitrous  acid  itself  is  not  known,  though  its  salts  are 
well  known.  When  a  strong  acid  is  added  to  a  solution  of 
a  nitrite,  the  salt  is  decomposed  and  nitrogen  trioxide  or 
nitrous  anhydride,  N203,  is  given  off.  The  reaction  will 
be  readily  understood.  The  tendency  of  the  strong  acid  is 
to  set  the  weak  acid  free,  as  when  sodium  chloride  is  treated 
with  sulphuric  acid,  and  potassium  nitrate  is  treated  with 
sulphuric  acid.  Were  the  action  in  this  case  analogous,  it 
would  be  represented  thus  : 

2KN02  +  H2S04  =  K2S04  +  2HN02. 

We  should  get  nitrous  acid  ;  but  instead  of  this  we  get 
a  substance  which  is  nitrous  acid  less  the  elements  of 
water  : 

N203  +  H20. 


Tl^is  tendency  on  the  part  of  compounds  which  contain 
hydrogen  and  oxygen  to  decompose  with  formation  of  water 
is  very  commonly  observed.  We  have  already  had  to  deal 
with  a  case  of  the  kind  in  ammonium  hydroxide.  This 
substance,  which  probably  exists  in  solution  in  water,  yields 
when  heated,  ammonia  and  water.  Many  compounds 
which  do  not  break  up  in  this  way  at  ordinary  tempera- 


156  INTRODUCTION  TO  CHEMISTRY. 

tures  do  so  at  elevated  temperatures.  This  decomposition 
is  to  be  ascribed  to  the  strong  affinity  of  hydrogen  for  oxy- 
gen. In  complex  compounds  several  forces  are  at  work  to 
keep  the  constituents  in  equilibrium.  If  the  affinity  of 
hydrogen  for  oxygen  is  much  stronger  than  the  other  forces 
at  work,  the  equilibrium  is  disturbed,  and  decomposition 
takes  place.  At  least,  this  is  the  thought  which  naturally 
suggests  itself  by  way  of  partial  explanation  of  the  phe- 
nomena. 

Anhydrides.  —  A  compound  which,  in  its  composition, 
bears  to  an  acid  the  relation  which  nitrogen  trioxide,  NaOs, 
bears  to  nitrous  acid,  HNOa,  is  called  an  anhydride.  Thus 
we  have  nitrous  anhydride,  N,03;  nitric  anhydride,  NaOB, 
etc.  Nitric  anhydride  bears  the  same  relation  to  nitric  acid 
that  nitrous  anhydride  bears  to  nitrous  acid. 


N306  +  HaO  =  2HNO.. 

In  more  general  terms,  it  may  be  said  that  any  oxide 
which,  when  brought  together  with  water,  forms  an  acid  by 
direct  combination,  is  an  anhydride.  We  shall  meet  with 
some  other  examples  of  this  class  of  compounds  further  on. 

The  Oxides  of  Nitrogen.  —  In  the  account  given  above  of 
the  transformations  of  nitric  acid  under  the  influence  of 
reducing  agents,  five  compounds  of  nitrogen  and  oxygen 
were  mentioned.  These  are  nitrogen  peroxide,  N02;  nitric 
oxide,  NO;  nitrous  oxide,  NaO;  nitrous  anhydride,  "N^O,, 
and  nitric  anhydride,  N205.  Arranging  these  compounds 
in  a  series,  beginning  with  that  one  which  contains  the 
smallest  proportion  of  oxygen,  and  considering  in  each  case 
the  quantity  of.  oxygen  which  is  combined  with  two  com- 
bining weights  (i.e.,  twenty-eight  parts  by  weight)  of  nitro- 


NITROUS  OXIDE.  157 

gen,  we  see  that  the  series  affords  a  striking  illustration  of 
the  facts  from  which  the  law  of  multiple  proportions  is  de- 
duced. The  series  is: 

Nitrous  oxide N20 

Nitric  oxide NO  or  N30a 

Nitrogen  trioxide N203 

Nitrogen  peroxide N0a  or  N204 

Nitric  anhydride N206 

It  will  be  seen  that  the  quantities  of  oxygen  combined 
with  twenty-eight  parts  of  nitrogen  are  16,  32,  48,  64,  and 
80. 

[What  other  series  of  compounds  have  we  already  had  to 
deal  with  which  illustrates  the  law  of  multiple  proportions 
almost  equally  strikingly?] 

Of  the  oxides  of  nitrogen,  only  three  need  be  considered, 
and  after  what  has  already  been  said  they  need  be  considered 
only  briefly. 

Nitrous  Oxide,  N20. — This  compound  is  formed  by  reduc- 
tion of  nitric  acid  when  the  acid  acts  upon  metals'  and  the 
degree  of  concentration  and  the  temperature  are  favorable. 
It  is  usually  prepared  by  heating  ammonium^  nitrate, 
NH4N03.  The  decomposition  takes  place  as  represented, 
thus: 

NH4NO,  =  N20  +  2H.O, 

the  products  being  nitrous  oxide  and  water.  In  this  reac- 
tion we  see  exhibited  the  tendency  of  hydrogen  and  oxygen 
to  combine  at  elevated  temperature.  At  ordinary  temper- 
atures this  affinity  is  not  strong  enough  to  cause  a  dis- 
turbance of  the  equilibrium  of  the  parts  of  the  compound. 


158  INTRODUCTION  TO  CHEMISTRY. 

As  the  temperature  is  elevated  it  becomes  stronger  and 
stronger,  until  finally  they  combine  and  the  decomposition 
above  represented  takes  place. 

EXPERIMENT  84. — In  a  retort  heat  10  to"  15  grams  crys- 
tallized ammonium  nitrate  until  it  has  the  appearance  of 
boiling.  Do  not  heat  higher  than  is  necessary  to  secure  a 
regular  evolution  of  gas.  Connect  a  wide  rubber  tube  di- 
rectly with  the  neck  of  the  retort  and  collect  the  evolved 
gas  over  water,  as  in  the  case  of  oxygen.  It  supports  com- 
bustion almost  as  well  as  pure  oxygen.  Try  experiments 
with  wood,  a  candle,  and  a  piece  of  phosphorus. 

The  gas  is  colorless  and  transparent.  It  has  a  slightly 
sweetish  taste.  It  is  somewhat  soluble  in  water,  so  that 
when  collected  over  water  there  is  always  considerable  loss. 
When  inhaled  it  causes  a  kind  of  intoxication,  which  is 
apt  to  show  itself  in  the  form  of  hysterical  laughing. 
Hence  the  gas  is  generally  known  as  laughing-gas.  In- 
haled in  larger  quantity  it  causes  unconsciousness  and  in- 
sensibility to  pain.  It  is  therefore  used  to  prevent  pain  in 
minor  surgical  operations,  as,  for  example,  in  pulling 
teeth. 

Nitric  Oxide,  NO. — This  gas,  as  has  been  stated,  is 
formed  when  nitric  acid  acts  upon  some  metals,  as  copper. 
The  action  is  believed  to  involve  two  changes. 

(1)  The  copper  displaces  the  hydrogen  of  the  acid,  and 
copper  nitrate  is  formed;  and 

(2)  The  hydrogen  acts  upon  the  nitric  acid,  reducing  it 
and  forming  nitric  oxide. 

These  two  stages  are  represented  thus: 

2HN03  +  On  =  Cu(N03)2  +  2E;  and 
2HN03  +  6H  =  4HaO  +  2NO. 


NITRIC  OXIDE.  159 

The  two  equations  may  be  combined  in  one,  when  we 
have 

8HN09  +  3Cu  =  3Cu(N03)2  +  4H20  +  2NO. 

EXPERIMENT  85. — Arrange  an  apparatus  as  shown  in 
Fig.  35.  In  the  flask  put  a  few  pieces  of 
copper  foil.  Cover  this  with  water.  Now 
add  slowly,  waiting  each  time  for  the  action 
to  begin,  ordinary  concentrated  nitric  acid. 
When  enough  nitric  acid  has  been  added  gas 
will  be  evolved.  If  the  acid  is  added  rapidly, 
it  not  unfrequently  happens  that  the  evolution 
of  gas  takes  place  too  rapidly,  so  that  the 
liquid  is  forced  out  of  the  flask  through  the 
funnel-tube.  This  can  be  avoided  by  not  be- 
ing in  a  hurry.  At  first  the  vessel  becomes 
filled  with  a  reddish-brown  gas,  but  soon  the  FlG- 55- 
gas  evolved  becomes  colorless.  Collect  over  water  two  01 
three  vessels  full.  The  gas  collected  is  principally  nitric 
oxide,  NO,  though  it  is  frequently  mixed  with  a  consider- 
able quantity  of  nitrous  oxide. 

Nitric  oxide  is  a  colorless,  transparent  gas.  Its  most  re- 
markable property  is  its  power  to  combine  directly  with 
oxygen  when  the  two  are  brought  together.  The  act  of 
combination  is  not  accompanied  by  the  appearance  of  light, 
though  heat  is  evolved.  The  reaction  which  takes  place  is 
represented  by  the  equation 

NO  +  0  =  N0a. 

The  product  is.  nitrogen  peroxide,  and   this  at  ordinary 
temperatures  is  a  reddish-brown  gas. 

EXPERIMENT  86. — Turn  one  of  the  vessels  containing 


160  INTRODUCTION  TO  CHEMISTRY. 

colorless  nitric  oxide  with  the  mouth  upward  and  uncover 
it.  The  colored,  gas  is  at  once  seen,  presenting  a  very 
striking  appearance.  Do  not  inhale  the  gas.  Perform  the 
experiments  with  nitric  oxide  where  there  is  a  good  draught. 

Nitric  oxide  does  not  burn,  and  does  not  support  com- 
bustion. When  we  consider  the  fact  that  nitrous  oxide, 
NS0,  supports  combustion  almost  as  well  as  oxygen,  it  ap- 
pears strange  that  another  compound  of  nitrogen  and  oxy- 
gen, containing  twice  as  much  oxygen  relatively  to  the  same 
quantity  of  nitrogen,  should  not  support  combustion.  This 
is  to  be  explained  by  the  relative  stability  of  the  two  com- 
pounds. In  the  case  of  nitrous  oxide,  the  oxygen  is  not 
firmly  held  in  combination;  the  equilibrium  established  be- 
tween the  forces  at  work  is  not  a  stable  one.  Hence,  when 
a  substance  which  has  a  strong  affinity  for  oxygen  is  brought 
in  contact  with  it,  the  equilibrium  is  disturbed,  or  the  ox- 
ide is  decomposed.  On  the  other  hand,  in  nitric  oxide  the 
arrangement  of  the  parts  is  a  more  stable  one.  The  oxygen, 
although  present  in  larger  quantity  than  in  nitrous  oxide, 
is  held  more  firmly,  and  cannot  easily  be  extracted.  The 
gas  does  not  support  combustion. 

Nitrogen  Peroxide,  N02. — This  gas  is  made  by  direct 
combination  of  nitric  oxide  with  oxygen,  as  seen  in  the  last 
experiment.  It  has  a  disagreeable  smell  and  is  poisonous. 
It  gives  up  a  part  of  its  oxygen  quite  easily,  and  is  hence 
useful  as  an  oxidizing  agent.  We  shall  hereafter  see  that 
in  the  manufacture  of  sulphuric  acid  the  oxidizing  power 
of  nitrogen  peroxide  is  utilized  in  a  very  beautiful  and  in- 
teresting way.  When  it  gives  up  oxygen,  it  is  changed  to 
nitric  oxide,  NO.  If  air  is  present,  nitric  oxide  is  changed 
back  again  to  nitrogen  peroxide,  which  may  again  give  up 
oxygen,  again  yielding  nitric  oxide,  and  so  on  indefinitely. 


SUMMARY.  161 

It  will  thus  be  seen  that  these  oxides  of  nitrogen  may  be 
made  to  serve  the  purpose  of  transferring  oxygen  from  the 
air  to  other  substances. 

Summary. — The  simpler  nitrogen  compounds  are  niade 
either  from  ammonia  or  nitric  acid.  Ammonia  is  formed 
in  nature  by  the  spontaneous  decomposition  of  animal  sub- 
stances. It  is  also  formed  by  heating  substances  which 
contain  carbon,  hydrogen,  and  nitrogen.  The  principal 
source  is  the  "  ammoniacal  liquor"  of  the  gas-works. 

Nitric  acid  is  formed  in  nature  as  the  potassium  or  sodi- 
um salt,  by  the  action  of  certain  organisms  on  substances 
containing  nitrogen. 

Ammonia  is  prepared  from  an  ammonium  salt  by  treat- 
ing it  with  a  strong  base.  Ammonium  chloride  and  lime 
are  commonly  used. 

With  acids  ammonia  forms  salts  which  are  known  as  am- 
monium salts,  and  in  which  the  compound  NH4  is  sup- 
posed to  act  the  part  of  a  metal.  This  hypothetical  metal 
is  called  ammonium. 

Ammonia  consists  of  14  parts  of  nitrogen  to  3  parts  of 
hydrogen.  The  gases  are  combined  in  the  proportion  of  1 
volume  of  nitrogen  to  3  volumes  of  hydrogen.  The  4 
volumes  thus  combined  condense  to  2  volumes  of  ammonia. 

There  is  always  a  simple  relation  between  the  volumes  of 
combining  gases  and  the  volume  of  the  compound  formed. 

A  comparison  of  the  specific  gravities  of  the  gaseous  ele- 
ments shows  that  these  bear  to  one  another  the  same  rela- 
tion as  the  combining  weights. 

Nitric  acid  is  prepared  from  a  nitrate  by  treating  it  with 
sulphuric  acid.  It  is  comparatively  unstable,  giving  up 
oxygen  easily.  With  metals  it  yields  salts,  but  the  hydro- 
gen evolved  acts  upon  a  part  of  the  acid,  forming  reduction 
11 


162  INTRODUCTION  TO  CHEMISTRY. 

products,  among  which  are  nitrous  oxide,  N20;  nitric  ox- 
ide, NO;  nitrous  anhydride,  N208;  and  nitrogen  peroxide, 
N02.  Under  some  circumstances,  the  action  of  hydrogen 
may  even  go  far  enough  to  form  ammonia.  Nitrous  acid 
itself  is  unstable,  breaking  up  into  the  anhydride,  N30g, 
and  water. 

Anhydrides  are  substances  which,  when  brought  together 
with  water,  combine  with  it  to  form  acids. 

Though  nitrous  oxide  is  formed  by  reduction  of  nitric 
acid,  it  is  best  prepared  in  pure  condition  by  heating  am- 
monium nitrate.  It  supports  combustion  well. 

Nitric  oxide  is  made  by  reduction  of  nitric  acid,  by  treating 
copper  with  nitric  acid.  It  combines  directly  with  oxygen, 
forming  the  strongly  colored  and  disagreeable-smelling 
nitrogen  peroxide. 

Nitrogen  peroxide  gives  up  .a  part  of  its  oxygen  easily, 
and  is  hence  a  good  oxidizing  agent.  It  is  thus  reduced  to 
nitric  oxide,  which  in  the  air  takes  up  oxygen. 


CHAPTER  IX. 
CARBON. 

WEEK  most  substances  from  the  vegetable  or  animal 
kingdom  are  heated  to  a  sufficiently  high  temperature  they 
blacken,  and  afterwards,  if  heated  in  the  air,  they  burn  up, 
us  we  say.  When  we  consider  the  great  variety  of  substances 
found  in  living  things,  it  is  certainly  remarkable  that  nearly 
all  have  this  property  in  common.  It  is  due  to  the  fact 
that  nearly  all  animal  and  vegetable  substances  contain 
the  element  carbon,  When  they  are  heated  the  other  ele- 
ments present  are  first  driven  off  in  various  forms  of  com- 
bination, while  the  carbon  is  the  last  to  go.  If  the  heating 
is  carried  on  in  the  air,  the  carbon  finally  combines  with 
oxygen  to  form  a  colorless  gas — it  burns  up.  Carbon  is  the 
central  element  of  organic  nature.  There  is  not  a  living 
thing,  from  the  minutest  microscopic  animal  to  the  mam- 
moth, from  the  moss  to  the  giant  tree,  which  does  not  con- 
tain this  element  as  an  essential  constituent.  The  number 
of  the  compounds  which  it  forms  is  almost  infinite,  and 
they  present  such  peculiarities  that  they  are  commonly 
treated  under  a  separate  head,  "Organic  Chemistry."  There 
is  no  good  reason  for  this,  except  the  large  number  of  the 
compounds.  The  special  study  of  these  compounds  can 
hardly  be  profitable  to  those  who  are  in  the  earliest  stages 


164  INTRODUCTION  TO  CHEMISTRY. 

of  their  work  in  chemistry,  though,  at  the  proper  time,  it 
forms  an  extremely  valuable  branch  of  study.  For  our 
present  purpose  it  will  suffice  to  consider  the  chemistry  of 
the  element  itself,  and  of  a  few  of  its  more  important  sim- 
ple compounds. 

Occurrence. — From  what  has  already  been  said,  it  will  be 
seen  that  the  principal  form  in  which  carbon  occurs  in 
nature  is  in  combination  with  other  elements.  It  occurs 
not  only  in  living  things,  but  in  their  fossil  remains,  as  in 
coal.  Coal-oil,  or  petroleum,  the  formation  of  which  was 
in  some  way  connected  with  the  processes  involved  in  the 
formation  of  coal,  consists  of  a  large  number  of  compounds 
which  contain  only  carbon  and  hydrogen.  Most  products 
of  plant-life  contain  the  elements  carbon,  hydrogen,  and 
oxygen.  Among  the  more  common  of  these  products  may 
be  mentioned  sugar,  starch,  cellulose,  the  fats,  etc.  Most 
products  of  animal  life  contain  carbon,  hydrogen,  oxygen, 
and  nitrogen.  Among  them  may  be  mentioned  albumin, 
fibrin,  casein,  etc.  Carbon  occurs  in  the  atmosphere  in  the 
form  of  carbon  dioxide.  [What  evidence  have  we  had 
showing  the  presence  of  carbon  dioxide  in  the  air  ?] 
It  also  occurs  in  the  form  of  salts  of  carbonic  acid;  the 
carbonates,  which  are  widely  distributed,  forming  whole 
mountain -ranges.  Limestone,  marble,  and  chalk  are  cal- 
cium carbonate. 

Uncombined,  the  element  occurs  pure  in  two  very  differ- 
ent forms  in  nature:  (1)  As  diamond;  and  (2)  as  graphite, 
or  plumbago. 

Before  considering  the  evidence  which  leads  to  the  con- 
clusion that  diamond  and  graphite  are  only  modifications 
of  the  same  element,  and  that  while  closely  related  to  each 
other  they  are  also  equally  closely  related  to  charcoal,  it 


DIAMOND.— GRAPHITE.  165 

will  be  best  to  study  separately  the  properties  of  each  of 
these  three  substances. 

1.  Diamond. — The  diamond  is  found  in  but  few  places 
on  the  earth.     Practically  nothing  is  known  as  to  the  con- 
ditions which  gave  rise  to  its  formation.     The  celebrated 
diamond-beds  are  in  the  East  Indies,   Borneo,  Sumatra, 
Brazil,  Australia,  Mexico,  and  at  the  Cape  of  Good  Hope. 
When  found,  diamonds  are  covered  with  an  untransparent 
layer,  which  must  be  removed  before  the  beautiful  properties 
are  apparent.     The  crystals  are  sometimes  what  are  known 
as  octahedrons;  that  is  to  say,  they  are  regular  eight-sided 
figures,  though  usually  they  are  somewhat  more  compli- 
cated.    It  is  the  hardest  substance  known. 

If  heated  to  a  very  high  temperature  without  access  of 
air,  it  swells  up  and  is  converted  into  a  black  mass  re- 
sembling graphite.  This  change  takes  place  without  loss 
in  weight.  Heated  to  a  high  temperature  in  oxygen,  it 
burns  up,  yielding  only  carbon  dioxide.  It  is  insoluble  in 
all  known  liquids. 

2.  Graphite. — Graphite,  or  plumbago,  is  found  in  nature 
in  large  quantities.     Sometimes  it  is  crystallized,  but  in 
forms  entirely  different  from  those  assumed  by  the  diamond. 
It  can  be  prepared  artificially  by  dissolving  charcoal  in 
molten  iron,  from  which  solution,  on  cooling,  it  is  deposit- 
ed as  graphite.     It  has  a  grayish-black  color  and  a  metallic 
lustre.     It  is  quite  soft,  leaving  a  leaden-gray  mark  on  paper 
when  drawn  across  it,  and  is  hence  used  in  the  manufac- 
ture of  so-called  lead  pencils.    It  is  sometimes  called  black- 
lead. 

When  heated  without  access  of  air  it  remains  unchanged. 
Heated  to  a  very  high  temperature  in  the  air,  or  in  oxygen, 


166  INTRODUCTION  TO  CHEMISTRY. 

it  burns  up,  forming  only  carbon  dioxide.   Like  the  diamond, 
it  is  insoluble  in  all  known  liquids. 

3.  Amorphous  Carbon. — All  forms  of  carbon  which  are 
not  diamond,  nor  graphite,  are  included  under  the  name 
amorphous  carbon.  The  name  signifies  simply  that  it  is 
not  crystallized.  The  most  common  form  of  amorphous 
carbon  is  ordinary  charcoal. 

Charcoal  is  that  form  of  carbon  which  is  made  by  the 
charring  process,  which  consists  simply  in  heating  without 
a  free  supply  of  air  to  effect  complete  combustion.  The 
substance  almost  exclusively  used  in  the  manufacture  oi 
charcoal  is  wood.  As  has  already  been  stated,  wood  is 
made  of  a  large  number  of  substances,  nearly  all  of  which, 
however,  consist  of  the  three  elements  carbon,  hydrogen, 
and  oxygen.  One  of  the  chief  constituents  of  all  kinds  of 
wood  is  cellulose.  Now,  when  we  set  fire  to  a  piece  of  wood, 
— that  is  to  say,  when  we  heat  it  up  to  the  temperature  ai 
which  oxygen  begins  to  act  on  it, — it  burns,  if  air  is  present. 
The  chemical  changes  which  take  place  are  complex  under 
ordinary  circumstances;  but  if  care  be  taken,  the  combus- 
tion can  be  made  complete,  when  all  the  carbon  is  converted 
into  carbon  dioxide,  and  all  the  hydrogen  into  water.  If, 
on  the  other  hand,  the  air  be  prevented  from  coming  in 
contact  with  the  wood  in  sufficient  quantity  to  effect  com- 
plete combustion,  the  hydrogen  is  given  off  partly  as  water 
and  partly  in  the  form  of  volatile  compounds  containing 
carbon  and  oxygen.  The  carbon,  however,  is  mainly  left 
behind  as  charcoaf,  as  there  is  not  enough  oxygen  to  con- 
vert it  into  carbon  dioxide. 

The  above  statements  will  enable  the  student  to  under- 
stand the  working  of  a  charcoal-kiln.  This  consists  essen, 
tially  of  a  pile  of  wood  so  arranged  as  to  leave  spaces  be- 


CHARCOAL.  167 

tween  the  pieces.  The  pile  is  covered  with  some  rough 
material  through  which  the  air  will  not  pass  easily,  as,  for 
example,  a  mixture  of  powdered  charcoal,  turf,  and  earth. 
Small  openings  are  left  in  this  covering  so  that  after  it  is 
kindled  the  wood  will  continue  to  burn  slowly.  The 
changes  above  mentioned  take  place,  the  gases  or  volatile 
substances  passing  out  of  the  top  of  the  kiln,  and  appearing 
as  a  thick  smoke.  In  due  time  the  holes  through  which 
the  air  gains  access  to  the  wood,  and  which  also  make  the 
burning  possible,  are  stopped  up,  and  the  burning  stops. 
Charcoal,  which  is  impure  amorphous  carbon,  is  left  be- 
hind. As  wood  always  contains  some  incombustible  sub- 
stances in  small  quantity,  these  are,  of  course,  found  in  the 
charcoal.  When  the  wood  or  charcoal  is  burned,  these  sub- 
stances remain  behind  as  the  ash. 

Ordinary  charcoal  is  a  black,  comparatively  soft  substance. 
It  burns  in  the  air,  though  not  easily,  unless  the  gases  which 
are  formed  are  constantly  removed  and  fresh  air  is  supplied, 
— conditions  which  are  met  by  a  good  draught,  or  by  blow- 
ing upon  the  fire  with  a  bellows.  It  burns  readily  in  oxy- 
gen, as  we  have  seen  (Experiment  22).  The  product  of  the 
combustion  in  oxygen  and  in  air,  when  the  conditions  are 
favorable,  is  carbon  dioxide,  C02.  In  the  air,  when  the 
draught  is  bad,  another  compound  of  carbon  and  oxygen, 
carbon  monoxide,  CO,  is  formed.  Heated  without  access 
of  air,  charcoal  remains  unchanged.  Charcoal  is  insoluble 
in  all  known  liquids. 

Besides  wood  charcoal,  there  are  other  forms  of  amorphous 
carbon,  which  are  manufactured  for  special  purposes,  or  are 
formed  in  processes  carried  on  for  the  sake  of  other  pro- 
ducts. Coke  is  a  form  of  amorphous  carbon  which  is  made 
by  heating  ordinary  gas  coal  without  access  of  air,  as  is 


168  INTRODUCTION  TO  CHEMISTRY. 

done  on  a  large  scale  in  the  manufacture  of  illuminating 
gas.  Coke  bears  to  coal  about  the  same  relation  that  char- 
coal bears  to  wood. 

Lamp-black  is  a  very  finely  divided  form  of  charcoal 
which  is  deposited  on  cold  objects  placed  in  the  flames  of 
burning  oils.  The  oils  consist  almost  exclusively  of  carbon 
and  hydrogen.  When  burned  in  the  air  they  yield  carbon 
dioxide  and  water.  If  the  flame  be  cooled  down  by  any 
means,  or  if  the  supply  of  air  be  partly  cut  off,  the  carbon 
is  not  completely  burned;  the  flame  "  smokes/'  as  we  say, 
and  deposits  soot.  This  soot  is  largely  made  up  of  fine 
particles  of  carbon.  It  is  used  in  .the  manufacture  of 
printer's-ink.  Carbon  is  acted  upon  directly  by  very  few 
substances,  and  is  not  soluble,  so  that  it  is  impossible  to 
destroy  the  color  of  printer's-ink  without  destroying  the 
material  upon  which  it  is  impressed. 

Bone-black,  or  Animal  Charcoal,  is  a  form  of  amorphous 
carbon  which  is  made  by  charring  bones.  Unless  treated 
with  an  acid  it  contains  the  incombustible  substances  con- 
tained in  bone,  as  calcium  phosphate,  etc. 

Bone-black  and  wood-charcoal  are  very  porous  and  have 
the  power  to  absorb  gases.  When  placed  in  air  containing 
bad-smelling  gases,  these  are  absorbed  and  the  air  thus 
purified.  When  water  which  contains  disagreeable  sub- 
stances is  treated  with  charcoal,  these  are  wholly  or  partly 
absorbed  and  the  water  improved.  Charcoal-filters  are 
therefore  extensively  used.  A  charcoal-filter  to  be  efficient 
should  be  of  good  size,  and  from  time  to  time  the  charcoal 
should  be  taken  out  and  renewed.  The  small  filters  which 

are  screwed  into  faucets  are  of  little  value,  as  the  charcoal 

• 

soon  becomes  charged  with  any  objectionable  material 
which  may  be  present  in  the  water. 


CHARCOAL.  169 

Some  coloring  matters  may  be  removed  from  liquids  by 
passing  the  liquids  through  bone-black  filters.  On  the  large 
scale,  this  fact  is  taken  advantage  of  in  the  refining  of 
sugar.  The  solution  of  sugar  first  obtained  from  the  cane 
or  beet  is  highly  colored;  and  if  it  were  evaporated,  the 
sugar  deposited  from  it  would  be  dark-colored.  If,  how- 
ever, the  solution  be  first  passed  through  bone-black  filters, 
the  color  is  removed,  and  now,  on  evaporating,  white  sugar 
is  deposited.  In  the  laboratory  constant  use  is  made  of  this 
method  for  the  purpose  of  purifying  liquids. 

EXPERIMENT  86a. — Make  a  filter  of  bone-black  by  fitting 
a  paper  filter  into  a  funnel  12  to  15  mm.  (5  to  6  inches)  in 
diameter  at  its  mouth.  Half -fill  this  with  bone-black. 
Make  a  dilute  solution  of  indigo.  Pour  it  through  the  filter. 
If  the  conditions  are  right  the  solution  will  pass  through 
colorless. — Do  the  same  thing  with  a  dilute  solution  of  lit- 
mus.— If  the  color  is  not  completely  removed  by  one  filter- 
ing, filter  it  again.  —  The  color  may  also  be  removed 
from  solutions  by  putting  some  bone-black  into  them  and 
boiling  for  a  time. — Try  this  with  half  a  litre  each  of  the 
litmus  and  indigo  solutions  used  in  the  first  part  of  the 
experiment.  Use  about  4  to  5  grams  bone-black  in  each 
case.  Shake  the  solution  frequently  while  heating. 

Charcoal  does  not  undergo  decay  in  the  air  or  under 
water  nearly  as  readily  as  wood.  That  is  another  way  of 
stating  the  chemical  fact  that  the  substances  of  which 
wood  are  made  up  are  more  susceptible  to  the  action  of 
other  chemical  substances  than  charcoal  is.  We  have  one 
illustration  of  this,  indeed,  in  the  relative  ease  with  which 
charcoal  and  wood  burn  in  the  air.  Piles  which  are  driven 
below  the  surface  of  water  are  charred  to  protect  them  from 
the  action  of  those  substances  which  cause  decay. 


170  INTRODUCTION  TO   CHEMISTRY. 

Coal. — Under  this  bead  are  included  a  great  many  kinds 
of  impure  amorphous  carbon  which  occur  ready-formed  in 
nature.  Although  we  might  distinguish  between  an  almost 
infinite  number  of  kinds  of  coal,  for  ordinary  purposes  they 
are  separated  into  hard  and  soft  coals,  or  anthracite  and 
bituminous  coals.  Then  there  are  substances  more  nearly 
allied  to  wood  called  lignite,  and  those  which  represent  a 
very  early  stage  in  the  process  of  coal-formation,  viz.,  peat. 

A  close  examination  of  all  these  varieties  has  shown  that 
they  have  been  formed  by  the  gradual  decomposition  of 
vegetable  material  in  an  insufficient  supply  of  air.  The  pro- 
cess has  been  going  on  for  ages.  Sometimes  the  substances 
have,  at  the  same  time,  been  subjected  to  great  pressure,  as 
can  be  seen  from  the  position  in  which  they  occur  in  the 
earth.  The  products  in  the  earlier  stages  of  the  coal-form- 
ing process  would  be  more  closely  allied  to  wood  than  those 
formed  in  the  later  stages. 

All  forms  of  coal  contain  other  substances  in  addition  to 
the  carbon.  The  soft  coals  are  particularly  rich  in  other 
substances.  When  heated  they  give  off  a  mixture  of  gases 
and  the  vapors  of  volatile  liquids.  The  gases  are,  for  the 
most  part,  useful  for  illuminating  purposes.  The  liquids 
form  a  black,  tarry  mass  known  as  coal-tar,  from  which  are 
obtained  many  valuable  compounds  of  carbon.  The  gases 
are  passed  through  water  for  the  purpose  of  removing  cer- 
tain impurities.  This  water  absorbs  ammonia  and  forms 
the  ammoniacal  liquor  of  the  gas-works,  which,  as  has  been 
stated,  is  the  principal  source  of  ammonia. 

Diamond,  Graphite,  and  Charcoal  Different  Forms  of  the 
Element  Carbon. — According  to  what  we  learned  in  the  first 
chapter,  an  element  is  a  form  of  matter  which  cannot  be 
decomposed  into  simpler  forms  by  any  means  now  known 


FORMS  OF  CARBON.  171 

to  chemists.  From  hydrogen  we  can  get  nothing  but  hy- 
drogen, except  by  bringing  it  together  with  some  other 
element ;  from  nitrogen  we  can  get  nothing  but  nitrogen, 
etc.  In  the  case-of  carbon,  however,  it  is  possible  for  the 
element  to  appear  in  three  forms,  which  differ  markedly 
from  one  another.  It  is  difficult  to  conceive  that  the  soft, 
black  charcoal  and  the  dull,  gray,  soft  graphite  are  chemi- 
cally identical  with  the  hard,  transparent,  brilliant 
diamond.  Yet  this  is  undoubtedly  the  case,  as  can  be 
proved  by  a  very  simple  experiment.  Each  of  the  sub- 
stances when  burned  in  oxygen  yields  carbon  dioxide. 
Now,  the  composition  of  carbon  dioxide  is  known,  so  that 
if  we  know  the  weight  of  carbon  dioxide  formed  in  any 
given  case,  we  know  also  the  weight  of  carbon  contained  in 
it.  If  we  burn  the  same  weights  of  diamond,  of  graphite, 
and  of  charcoal,  we  find  that  the  same  quantity  of  carbon 
dioxide  is  formed  in  each  case,  and  in  each  case  the  weight 
of  the  carbon  contained  in  the  carbon  dioxide  formed  is 
equal  to  the  weight  of  substance  burned. 

[PROBLEM. — How  much  carbon  dioxide,  CO2,  should  be  ob- 
tained by  burning  0.5  gram  diamond  ?  The  combining  weight 
of  carbon  is  12.] 

Notwithstanding  the  marked  differences  in  their  appear- 
ance, the  three  forms  of  carbon  have,  as  we  have  seen,  some 
properties  in  common.  They  are  insoluble  in  all  known 
liquids.  They  are  tasteless  and  inodorous.  They  are  in- 
fusible. When  heated  without  access  of  air,  they  remain 
unchanged,  unless  the  temperature  is  very  high. 

That  one  and  the  s;ime  substance  can  appear  in  markedly 
different  forms  under  different  conditions  is  seen  in  the 
case  of  water.  Hail  and  snow  would  hardly  be  suspected 


INTRODUCTION  TO  CHEMISTRY. 

of  being  the  same  substance  by  one  who  was  not  quite 
familiar  with  them.  The  difference  in  this  case,  as  in  that 
which  we  have  been  considering,  is  believed  to  be  due  to  the 
way  in  which  the  small  particles  of  which  the  substances 
are  made  up  are  arranged  with  reference  to  one  another. 
If  we  had  a  number  of  small  pieces  of  wood  all  of  the  same 
size  and  shape,  say  cubical,  and  should  carefully  arrange 
these  in  some  regular  way,  we  might  easily  make  a  com- 
paratively compact  mass  of  them,  and  the  mass  would  have 
a  regular  form.  We  might  arrange  them,  further,  in  a 
second  way  with  regularity.  And  we  might  simply  throw 
the  pieces  together  in  a  jumble.  These  three  kinds  of  ar- 
rangement would  represent,  in  a  rough  way,  the  difference 
between  the  three  forms  of  carbon.  Each  pile  would  be 
made  of  wood,  but  still  in  outward  appearance  they  would 
differ  from  one  another. 

Chemical  Conduct  of  Carbon. — At  ordinary  temperatures 
carbon  is  an  inactive  element.  If  it  be  left  in  contact 
with  any  one  of  the  elements  thus  far  considered, — viz., 
hydrogen,  oxygen,  chlorine,  and  nitrogen, — no  change  takes 
place.  Indeed,  unless  the  temperature  be  raised  it  will 
not  combine  with  any  other  elements.  At  higher  tempera- 
tures, however,  it  has  marked  affinity  for  other  elements, 
especially  for  oxygen.  Under  proper  conditions  it  combines 
also  with  nitrogen,  with  hydrogen,  and  with  many  other 
elements.  It  combines  with  oxygen  either  directly,  as  when 
it  burns  in  the  air  or  in  oxygen;  or  it  abstracts  oxygen  from 
some  of  the  oxides. 

The  direct  combination  of  carbon  and  oxygen  has 
already  been  shown  in  Experiment  22,  and  is  familiar  to 
every  one  in  the  fire  in  a  charcoal  furnace.  That  carbon 
dioxide  is  the  product  may  be  shown  by  passing  the  gas 


CHEMICAL  CONDUCT  OF  CARSON. 


173 


into  lime-water  or  baryta- water,  when  insoluble  calcium,  or 
barium  carbonate,  will  be  thrown  down. 

EXPERIMENT  87. — Put  a  small  piece  of  charcoal  in  a 
piece  of  hard  glass  tube.  Pass  oxygen  through  the  tube,  at 
the  same  time  heating  it.  Pass  the  gases  into  clear  lime- 
water.  Arrange  the  apparatus  as  shown  in  Fig.  36.  • 


A  is  a  large  bottle  containing  oxygen;  B  is  a  cylinder 
containing  sulphuric  acid;  C  is  a  U-tube  containing  calcium 
chloride  ;  D  is  the  hard  glass  tube  containing  the  charcoal; 
E  is  the  cylinder  with  clear  lime-water.  In  what  previous 
experiment  was  this  method  of  showing  the  formation  of 
carbon  dioxide  used  ?  The  reason  why  it  is  used  is  simply 
that  an  insoluble  compound  is  formed,  and  this  can  be 
seen,  and  it  can  be  separated  from  the  liquid  and  examined. 
The  reaction  which  takes  place  is  represented  thus  : 


Ca02H2 

Lime, 


C02  CaC03     +     HaO. 

Calcium  carbonate. 


Carbon  dioxide. 


No  other  common  gas  acts  in  this  way  on  lime-water. 
Hence,  when,  under  ordinary  circumstances,  a  gas  is  passed 


174  INTRODUCTION  TO  CHEMISTRY. 

into  lime-water  and  an  insoluble  substance  is  formed,  we 
may  conclude  that  the  gas  is  carbon  dioxide. 

The  abstraction  of  oxygen  from  compounds  by  means  of 
carbon  may  be  illustrated  in  a  number  of  ways. 

EXPERIMENT  88. — Mix  together  2  or  3  grams  powdered 
copper  oxide,  CuO,  and  about  one  tenth  its  weight  of 
powdered  charcoal ;  heat  in  a  tube  to  which  is  fitted  an 
outlet  tube,  as  shown  in  Fig.  37. 

Pass  the  gas  which  is  given  off 
into  lime-water  contained  in  a 
test-tube.  Is  it  carbon  dioxide  ? 
What  evidence  have  you  that 
oxygen  has  been  extracted  from 
the  copper/ oxide  ?  What  is  the 
appearance  of  the  substance  left 
in  the  tube  ?  Does  it  suggest  the 
metal  copper  ?  Treat  a  little  of 
-  37,  it  with  strong  nitric  acid.  What 

should  take  place  if  the.  substance  is  metallic  copper  ? 
(See  Experiment  79.)  What  does  take  place?  The  reac- 
tion between  the  charcoal  and  the  copper  oxide  is  repre- 
sented thus  : 

2CuO  +  0  =  2Cu  -f  C02. 

EXPERIMENT  89. — Perform  a  similar  experiment  with  a 
little  white  arsenic  in  a  small  glass  tube  closed  at  one  end. 
Take  about  equal  parts  of  charcoal  and  arsenic.  White 
arsenic  is  a  compound  of  the  element  arsenic  and  oxygen,  of 
the  composition  represented  by  the  formula  As203.  The 
reaction  which  takes  place  when  it  is  heated  with  charcoal 
is  represented  thus: 

2Asa03  +  3C  =  4As  +  3C08. 


CARBON  A  REDUCING  AGENT.  175 

The  element  arsenic  formed  is  volatile,  and  is  hence 
driven  out  of  the  bottom  of  the  tube  and  deposited  on  the 
walls  above  the  mixture  in  the  form  of  a  mirror  with  a  me- 
tallic lustre. 

The  abstraction  of  oxygen  from  a  compound  is  known  as 
reduction,  as  has  already  been  explained.  Hence  carbon  is 
called  a  reducing  agent.  It  is  indeed  the  reducing  agent 
which  is  most  extensively  used  in  the  arts.  Its  chief  use  is 
in  extracting  metals  from  the  ores,  which  are  the  forms  in 
which  they  occur  in  nature.  Thus,  iron  does  not  occur  in 
nature  as  iron,  but  in  combination  with  other  elements, 
especially  with  oxygen.  In  order  to  get  the  metal,  the  ore 
must  be  reduced,  or,  in  other  words,  the  oxygen  must  be 
extracted.  This  is  invariably  accomplished  by  heating  it 
with  some  form  of  carbon,  either  charcoal  or  coke. 

[What  other  element  already  considered  acts  as  a  re- 
ducing agent?  Give  an  example  of  its  reducing  power.] 

The  elements  thus  far  considered,  with  the  exception  of 
carbon,  are  gases.  Carbon  is  not  known  in  the  form  of 
gas.  It  cannot  even  be  melted.  In  comparing  the  weights 
of  equal  volumes  of  the  gaseous  elements  it  will  be  found, 
as  has  been  found  in  the  case  of  hydrogen,  chlorine,  oxy- 
gen, and  nitrogen,  that  they  bear  to  one  another  the  same 
relations  as  the  combining  weights.  Whether  this  rule 
holds  good  in  regard  to  carbon,  we  cannot  say. 


CHAPTER  X. 

COMPOUNDS  OF  CARBON  WITH  HYDROGEN,  WITH  OXY- 
GEN, AND  WITH  NITROGEN. 

IN  the  laboratory  it  is  not  a  simple  matter  to  effect  com- 
bination between  carbon  and  hydrogen  except  in  a  few 
simple  cases.  In  nature  processes  are  in  operation  which 
give  rise  to  the  formation  of  a  large  number  of  compounds 
containing  these  elements;  and,  further,  in  one  branch  of 
manufacture,  the  preparation  of  illuminating  gas  from  coal, 
the  conditions  are  such  as  to  cause  the  combination  of  car- 
bon and  hydrogen,  several  interesting  compounds  being 
thus  formed.  There  are  no  other  two  elements  which  com- 
bine with  each  other  in  as  many  different  proportions  as  car- 
bon and  hydrogen.  The  compounds  thus  formed  are  known 
as  hydrocarbons.  The  number  of  hydrocarbons  known  is 
very  great,  being  somewhere  between  one  and  two  hundred. 
Fortunately,  investigation  has  shown  that  quite  simple  re- 
lations exist  between  these  compounds  ;  and  hence,  though 
the  number  is  large,  the  study  is  not  as  difficult  as  might 
be  expected. 

Petroleum  is  an  oily  liquid  found  in  many  places  in  the 
earth  in  large  quantity.  Its  formation  is  in  some  way  con- 
nected with  the  formation  of  coal.  In  the  earth  it  contains 
both  gases  and  liquids.  When  it  is  brought  into  the  air, 
the  pressure  being  removed,  the  gases  are  given  off.  There 


HYDROCARBONS.  177 

are  several  gases  given  off,  and  a  large  number  of  liquids 
left  behind.  The  simplest  gas  corresponds  to  the  formula 
CH4,  the  next  to  C2H6,  the  next  to  C3H8,  the  next  to 
C4H10.  An  examination  of  the  liquid  has  shown  it  to  con- 
tain other  hydrocarbons  of  the  formulas  CBH12,  06H14, 
07H16,  C8H18,  etc.  It  will  be  seen  that  these  compounds 
bear  a  simple  relation  to  one  another,  as  far  as  composition 
is  concerned.  Arranging  them  in  a  perpendicular  series 
we  have 

CH4,  Methane,  or  Marsh  gas; 

C2H6,  Ethane; 

C3H8,  Propane; 

04H10,  Butane; 

C6H12,  Pentane; 

C6H14,  Hexane; 

C7H16,  Heptane; 

C8H18,  Octane. 

The  first  member  of  th§  series  differs  from  the  second  by 
CH2;  there  is  also  this  same  difference  between  the  second 
and  third,  the  third  and  fourth,  and,  in  general,  between 
any  two  consecutive  members  in  the  series.  This  relation 
is  known  as  homology,  and  such  a  series  is  known  as  an 
homologous  series.  Carbon  is  distinguished  from  all  other 
elements  by  its  power  to  form  homologous  series. 

Besides  the  series  above  mentioned,  which,  as  its  simplest 
member  is  marsh  gas,  CH4,  is  known  as  the  marsh-gas 
series,  there  are  other  homologous  series  of  hydrocarbons. 
There  is  one  beginning  with  ethylene,  C,H4,  examples  of 
which  are 

Ethylene,  02H4; 
Propylene,  C3H8; 
Butylene,  C4H,. 
12 


178  INTRODUCTION  TO  CHEMISTRY. 

There  is  another  beginning  with  acetylene;<  C2Ha,  exam- 
ples of  which  are 

Acetylene,  C2H3; 
Allylene,  C3H4. 

Another  series  begins  with  benzene,  C6H6.  Some  of  the 
members  of  this  series  are 

Benzene,  C6H6; 
Toluene,  C7H8; 
Xylene,  C8H10. 

These  are  the  hydrocarbons  which  are  obtained  from  coal- 
tar. 

The  hydrocarbons  are  capable  of  undergoing  a  great 
variety  of  changes,  and  thus  yielding  a  great  many  'differ- 
ent products.  Among  the  products  thus  obtained  from 
the  hydrocarbons  and  closely  related  to  them  are  com- 
pounds known  as  alcohols,  ethers,  acids,  aldehydes,  etc. 
As  examples  of  alcohols,  wood-spirit,  or  methyl  alcohol, 
CH40,  and  spirits  of  wine,  or  ethyl  alcohol,  C2H60,  may  be 
mentioned.  Ordinary  ether,  or  ethyl  ether,  C4H100,  is  the 
best-known  example  of  the  class  of  compounds  called 
ethers.  Formic  acid  obtained  from  ants,  acetic  acid,  the 
acid  of  vinegar,  oxalic  acid,  and  tartaric  acid  are  examples 
of  the  acids. 

The  study  of  these  substances  is  simple  enough;  but  as 
the  relations  between  the  compounds  of  carbon  are  not 
met  with  to  any  extent  between  the  compounds  of  other 
elements,  the  interest  connected  with  them  is  rather  of  a 
special  character,  and  it  is  therefore  better  to  leave  their 
consideration  until  after  a  general  survey  of  the  field  of 
chemistry  has  been  made.  The  best  reason  for  this  course 
is,  perhaps,  that  the  study  of  the  compounds  of  the  other 
elements  is  a  better  preparation  for  the  more  special  study 


MARSH  GAS.  179 

of  the  compounds  of  carbon  than  the  study  of  the  com- 
pounds of  carbon  for  the  study  of  other  compounds.  For 
the  purpose  for  which  this  book  is  designed  it  appears  more 
profitable,  therefore,  to  confine  our  attention  here  to  a  few 
of  the  simplest  compounds  of  carbon. 

Marsh  Gas,  Methane,  Fire-Damp,  CH4. — Marsh  gas  is 
found  in  nature  in  petroleum,  and  is  given  off  when  the  oil 
is  taken  out  of  the  earth  and  the  pressure  is  removed.  It  is 
formed,  as  the  name  implies,  in  marshes,  as  the  product  of 
a  reducing  process.  Vegetable  matter  is  composed  of  carbon, 
hydrogen,  and  oxygen.  When  it  undergoes  decomposition  in 
the  air  in  a  free  supply  of  oxygen,  the  final  products  formed 
are  carbon  dioxide  and  water.  When  the  decomposition 
takes  place  without  access  of  oxygen,  as  under  water,  marsh 
gas,  which  is  a  i  eduction  product,  is  formed.  The  gas  can 
be  made  in  the  laboratory  by  passing  a  mixture  of  hydro- 
gen sulphide,  H2S,  and  the  vapor  of  carbon  bisulphide, 
CS2,  over  heated  copper.  The  sulphur  is  extracted  from 
the  compounds,  and  the  carbon  and  hydrogen  combine,  as 
represented  in  the  equation 

CS2  -f  2H2S  +  80u  =  CH4  +  40u2S. 

Marsh  gas  is  met  with  in  coal-mines,  and  is  known  to  the 
miners  as  fire-damp,  damp  being  the  general  name  applied 
to  a  gas,  and  the  name  fire-damp  meaning  a  gas  that  burns. 
To  prepare  it  in  the  laboratory,  it  is  most  convenient  to 
heat  a  mixture  of  sodium  acetate  and  quick-lime.  The 
change  which  takes  place  will  be  most  readily  understood 
by  considering  it  as  a  simple  decomposition  of  acetic  acid. 
Acetic  acid  has  the  formula  C2H402.  When  heated  alone, 
it  boils  and  does  not  suffer  decomposition.  If  it  be  con- 
verted into  a  salt,  and  heated  in  the  presence  of  a  base,  it 
breaks  up  into  marsh  gas  and  carbon  dioxide : 
C2H402  =  OH4  +  C0a. 


180  INTEODUGTION  TO  CHEMISTRY. 

The  carbon  dioxide,,  which  with  bases  forms  salts,  does  not 
pass  off,  but  remains  behind  in  the  form  of  a  salt  of  car- 
bonic acid. 

Marsh  gas  is  a  colorless,  transparent,  tasteless,  inodorous 
gas.  It  is  slightly  soluble  in  water.  It  burns,  forming 
carbon  dioxide  and  water.  When  mixed  with  air,  the 
mixture  explodes  if  a  flame  or  spark  comes  in  contact  with 
it.  This  is  one  of  the  causes  of  the  explosions  which  so 
frequently  occur  in  coal-mines.  To  prevent  these  explo- 
sions a  special  lamp  was  invented  by  Sir  Humphrey  Davy, 
which  is  known  as  Davy's  safety-lamp.  The  simple  prin- 
ciples involved  in  its  construction  will  be  explained  when 
the  subject  of  flame  is  considered. 

Ethylene,  Olefiant  Gas,  C2H4.  —  This  hydrocarbon  is 
formed  by  heating  a  mixture  of  ordinary  alcohol  and  con- 
centrated sulphuric  acid.  The  reaction  is  represented 
thus: 

C,H60  =  H,0  +  O.H.. 

Alcohol.  Et-hylene. 

Ethylene  is  a  colorless  gas,  which  can  be  condensed  to  a 
liquid.  It  burns  with  a  luminous  flame.  With  oxygen  it 
forms  an  explosive  mixture. 

Acetylene,  C2H2. — Acetylene  is  formed  when  a  current 
of  hydrogen  is  passed  between  carbon  poles,  which  are  in- 
candescent in  consequence  of  the  passage  of  a  powerful 
electric  current.  In  this  case  carbon  and  hydrogen  com- 
bine directly.  It  is  formed  also  when  the  flame  of  an  or- 
dinary laboratory  gas-burner  (Bunsen  burner)  "strikes 
back,"  or  burns  at  the  base  without  a  free  supply  of  air. 
Its  odor  is  unpleasant.  It  burns  with  a  luminous,  smoky 
flame. 

Carbon  Dioxide,  C02. — The  principal  compound  of  car- 
bon and  oxygen  is  carbon  dioxide,  C09,  commonly  known 


CARBON  DIOXIDE.  181 

as  carbonic-acid  gas.  Under  the  head  of  The  Atmosphere 
attention  was  called  to  the  fact  that  this  gas  is  a  constant 
constituent  of  the  air,  though  its  relative  quantity  is  small. 
It  issues  from  the  earth  in  many  places,  particularly  in  the 
neighborhood  of  volcanoes.  Many  mineral  waters  contain 
it  in  large  quantity,  as  the  waters* of  Pyrmont,  Setters,  and 
the  Geyser  Spring  at  Saratoga.  In  small  quantity  it  is 
present  in  all  natural  waters.  In  combination  with  bases 
it  occurs  in  enormous  quantities,  particularly  in  the  form 
of  calcium  carbonate,  CaC03,  varieties  of  which  are  ordi- 
nary limestone,  chalk,  marble,  and  calc-spar.  Dolomite, 
which  forms  mountain-ranges,  being  particularly  abundant 
in  the  Swiss  Alps,  is  a  compound  containing  calcium  car- 
bonate and  magnesium  carbonate,  MgC03. 

Carbon  dioxide  is  constantly  formed  in  many  natural 
processes.  Thus,  all  animals  that  breathe  in  the  air  give 
off  carbon  dioxide  from  their  lungs. 

EXPERIMENT  90. — Force  the  gases  from  the  lungs  through 
some  lime-water  by  means  of  an  apparatus  arranged  as 
shown  in  Fig.  38.    A  white,  insoluble  compound  is  formed. 
This  is  calcium  carbonate.    On 
addition   of    a  few   drops    of 
hydrochloric  acid  it  dissolves. 

That  carbon  dioxide  is 
formed  in  the  combustion  of 
charcoal  and  wood  has  already 
been  shown.  In  a  similar  way 
it  can  be  shown  that  the  gas  is 
formed  whenever  any  of  our 
ordinary  combustible  materials 
are  burned.  From  our  fires,  FIG.  38. 

as  from  our  lungs,  and  from  the  lungs  of  all  animals,  then, 


182  INTRODUCTION  TO  CHEMISTRY 

carbon  dioxide  is  constantly  given  off.  Further,  the  natu- 
ral processes  of  decay  of  both  vegetable  and  animal  mat- 
ter tend  to  convert  the  carbon  of  this  matter  into  car- 
bon dioxide,  which  is  then  spread  through  the  air.  The 
process  of  alcoholic  fermentation,  and  some  other  like  proc- 
esses, also  give  rise  to  the  formation  of  carbon  dioxide. 
In  all  fruit-juices  there  is  contained  sugar.  "When  the 
fruits  ripen,  fall  off,  and  undergo  spontaneous  change,  the 
sugar  is  changed  to  alcohol  and  carbon  dioxide. 

We  see,  thus,  that  there  are  many  important  sources  of 
supply  of  carbon  dioxide,  and  we  can  readily  understand 
why  the  gas  should  be  found  everywhere  in  the  air. 

Preparation  of  Ca-rbon  Dioxide.— The  easiest  way  to  get 
carbon  dioxide  unmixed  with  other  substances  is  to  add  an 
acid  to  a  carbonate.  Whenever  any  acid  is  added  to  any 
carbonate  there  is  an  evolution  of  gas. 

EXPERIMENT  91. — In  test-tubes  add  successively  dilute 
hydrochloric,  sulphuric,  nitric,  and  acetic  acids  to  a  little 
sodium  carbonate.  In  each  case  pass  the  gas  given  off 
through  lime-water;  and  insert  a  burning  stick  in  the  up- 
per part  of  each  tube. — Perform  the  same  experiment  with 
small  pieces  of  marble. 

In  the  decomposition  of  the  carbonates  or  salts  of  carbonic 
acid  by  other  acids,  we  see  exemplified  the  same  principle 
as  that  which  is  made  use  of  in  setting  nitric  acid  free  from 
a  nitrate,  or  hydrochloric  acid  from  sodium  chloride,  by 
means  of  sulphuric  acid.  The  strong  acid  appropriates  the 
metal  and  gives  up  its  hydrogen.  As  carbonic  acid  is  the 
weakest  acid,  it  is  set  free  from  its  salts  by  any  other  acid. 
When  any  acid,  say  hydrochloric  acid,  is  added  to  a  car- 
bonate, say  sodium  carbonate,  the  first  action  consists  in  an 


CARSON  DIOXIDE.  183 

exchange  of  the  hydrogen  of  the  acid  for  the  metal  of  the 
carbonate: 

Na2C03  +  2HC1  =  SNaCl  +  H2C03. 

If  sulphuric  acid  be  used,  the  reaction  is  represented  thus: 
Na.00,  +  H2S04  =  Na,S04  +  H2C03. 

This  reaction  is  analogous  to  that  which  takes  place  be- 
tween sodium  nitrate  and  sulphuric  acid  in  the  preparation 
of  nitric  acid: 

2NaN03  +  H2S04  =  Na2S04  +  2HN03. 

Carbonic  acid,  however,  is  an  unstable  substance,  and 
breaks  up  into  water  and  carbon  dioxide  as  soon  as  it  is  lib* 
erated  from  its  salts: 

H2C03  =  H20  +  C02. 

Hence,  whenever  a  carbonate  is  treated  with  an  acid,  car- 
bon dioxide  is  evolved. 

It  will  be  seen  that  the  decomposition  of  carbonic  acid 
into  carbon  dioxide  and  water  is  analogous  to  the  decompo- 
sition of  nitrous  acid,  HN02,  into  nitrogen  trioxide  and 
water;  and  similar  to  the  decomposition  of  ammonium  hy- 
droxide into  ammonia  and  water. 

[What  is  a  compound  called  which  bears  to  an  acid  the 
relation  which  carbon  dioxide  bears  to  carbonic  acid?] 

For  the  purpose  of  preparing  carbon  dioxide  in  the  lab- 
oratory, calcium  carbonate  in  the  form  of  marble,  or  lime- 
stone, and  hydrochloric  acid  are  commonly  used.  The  re- 
action involved  is  represented  thus: 

CaC03  -f  2H01  =  Cad,  +  C02  +  H20. 


184  INTRODUCTION  TO  CHEMISTRY. 

EXPERIMENT  92. — Arrange  an  apparatus  as  shown  in 
Fig.  39.  In  the  flask  put  some  pieces  of  mar- 
ble, or  lime-stone,  and  pour  ordinary  hydro- 
chloric acid  on  it.  The  gas  should  be  collected 
by  displacement  of  air,  the  vessel  being  placed 
with  the  mouth  upward,  as  the  gas  is  much 
heavier  than  air.  Collect  several  cylinders  or 
bottles  full  of  the  gas.  Into  one  introduce 
successively  a  lighted  candle,  a  burning  stick, 
a  bit  of  burning  phosphorus.  They  are  all  ex- 
tinguished. Into  another  put  a  live  mouse. 
With  another  proceed  as  if  pouring  water  from 
FIG.  39.  it.  Pour  the  invisible  gas  upon  the  flame  of  a 
btirning  candle.  Pour  some  of  the  gas  from  one  vessel  to 
another,  and  show  that  it  has  been  transferred.  Balance  a 
beaker  on  a  good-sized  scales,  and  pour  carbon  dioxide  into 
it.  If  the  balance  is  at  all  sensitive,  the  pan  on  which  the 
beaker  is  placed  will  go  down. 

Carbon  dioxide  is  a  colorless  gas  at  ordinary  temperature. 
When  subjected  to  a  low  temperature  and  high  pressure  it 
is  converted  into  a  liquid;  and  when  some  of  the  liquid  is 
exposed  to  the  air,  evaporation  takes  place  so  rapidly  that 
a  great  deal  of  heat  is  absorbed,  and  some  of  the  liquid  be- 
comes solid.  The  gas  has  a  slightly  acid  taste  and  smell. 
It  is  not  combustible,  nor  does  it  support  combustion. 
It  is  not  combustible  for  the  same  reason  that  water  is  not; 
because  it  already  holds  in  combination  all  the  oxygen  it 
has  the  power  to  combine  with.  Before  it  can  burn  again, 
it  must  first  be  decomposed.  Carbon  has  the  power  to 
combine  with  oxygen,  and  in  so  doing  it  gives  rise  to  the 
formation  of  a  definite  quantity  of  heat.  A  kilogram  of 
carbon  represents  a  certain  quantity  of  energy,  which  we 


CARSON  DTOXIDfl.  185 

can  get  first  in  the  form  of  heat  and  then  convert  into 
other  forms,  as  electricity,  motion,  etc.  After  the  kilo- 
gram of  carbon  has  been  burned,  it  no  longer  represents 
the  energy  it  did  in  the  form  of  carbon.  A  body  of  water 
elevated  ten  or  fifteen  feet  represents  a  certain  quantity  of 
energy  which  can  be  obtained  by  allowing  the  water  to  fall 
upon  the  paddles  of  a  water-wheel  connected  with  the  ma- 
chinery of  a  mill.  After  the  water  has  fallen,  however,  it 
no  longer  has  power  to  do  work,  or  it  has  no. energy.  In 
order  that  it  may  again  do  work,  it  must  again  be  lifted. 
Not  only  does  carbon  dioxide  not  burn,  but  it  does  not  sup- 
port combustion.  Although  it  contains  a  large  quantity  of 
oxygen  in  combination,  it  does  not  as  a  rule  give  it  up  to 
other  substances. 

[What  gas  containing  oxygen  in  combination  with 
another  element  does  support  combustion?] 

Carbon  dioxide  is  much  heavier  than  air,  its  specific 
gravity  being  1.529.  A  litre  of  the  gas  under  standard 
conditions  of  temperature  and  pressure  weighs  1.877  grams. 
It  dissolves  in  water,  one  volume  of  water  dissolving  about 
one  volume  of  the  gas  at  the  ordinary  temperature.  As  is 
the  case  with  all  gases  when  the  pressure  is  increased,  the 
water  dissolves  more  gas;  and  when  the  pressure  is  removed, 
the  gas  again  escapes.  The  so-called  "  soda-water"  is 
simply  water  charged  with  carbon  dioxide  under  pressure. 
The  escape  of  the  gas,  when  the  water  is  drawn,  is  familiar 
to  every  one.  The  carbon  dioxide  used  i-n  charging  the 
water  is  generally  made  from  a  sodium  salt  of  carbonic 
acid  known  as  "bicarbonate  of  soda." 

Respiration. — It  was  stated  above  that  carbon  dioxide  is 
given  off  from  the  lungs  just  as  it  is  from  a  fire,  and  the 
fact  was  demonstrated  by  means  of  a  simple  experiment. 


186  INTRODUCTION  TO  CHEMISTRY. 

It  is  a  waste  product  of  the  processes  going  on  in  the  ani- 
mal body.  Just  as  it  cannot  support  combustion,  so  also 
it  cannot  support  respiration.  It  is  not  poisonous  any  more 
than  water  is;  but  it  is  not  able  to  supply  the  oxygen  which 
is  needed  for  breathing  purposes,  and  hence  animals  die 
when  placed  in  it.  They  die  by  suffocation,  as  they  do  in 
drowning.  Any  considerable  increase  in  the  quantity  of  car- 
bon dioxide  in  the  air  above  that  which  is  normally  present 
is  objectionable,  for  the  reason  that  it  decreases  the  propor- 
tion of  oxygen  in  the  air  which  is  breathed.  If,  however, 
pure  carbon  dioxide  be  introduced  into  the  air,  it  has  been 
found  that  as  much  as  5  per  cent  may  be  present  without 
causing  injury  to  those  who  breathe  it.  In  a  badly  venti- 
lated room  in  which  a  number  of  people  are  collected  and 
lights  are  burning,  it  is  well  known  that  in  a  short  time  the 
air  becomes  foul,  and  bad  effects,  such  as  headache,  drowsi- 
ness, etc.,  are  produced  on  the  occupants  of  the  room. 
These  effects  have  been  shown  to  be  due,  not  to  the  carbon 
dioxide,  but  to  other  waste  products  which  are  given  off 
from  the  lungs  in  the  process  of  breathing.  The  gases 
given  off  from  the  lungs  consist  of  nitrogen,  oxygen,  carbon 
dioxide,  and  water  vapor.  Besides  these,  however,  there 
are  many  substances  in  a  fine  state  of  division  which  con- 
tain carbon,  and  are  in  a  state  of  decomposition.  These 
are  poisonous,  and  are  the  chief  cause  of  the  bad  effects  ex- 
perienced in  breathing  air  which  has  become  contaminated 
by  the  exhalations  from  the  lungs.  As  carbon  dioxide  is 
given  off  from  the  lungs  at  the  same  time,  the  quantity  of  this 
g;is  present  is  proportional  to  the  quantity  of  the  organic 
impurities.  Hence,  by  determining  the  quantity  of  carbon 
dioxide  we  are  enabled  to  form  a  judgment  as  to  whether 
the  air  of  a  room  occupied  by  human  beings  is  fit  for  use 


CARBON  DIOXIDE.  187 

or  not.  As  carbon  dioxide  is  formed  in  the  earth  wherever 
an  acid  solution  comes  in  contact  with  a  carbonate,  the  gas 
is  frequently  given  off  from  fissures  in  the  earth.  It  is 
hence  not  unfrequently  found  in  old  wells  which  have  not 
been  in  use  for  some  time,  and  deaths  have  been  caused  by 
descending  these  wells  for  the  purpose  of  repairing  them. 
The  gas  is  also  frequently  met  with  in  mines,  and  is  called 
choke-damp  by  the  miners.  The  miners  are  aware  that 
after  an  explosion  caused  by  fire-damp  there  is  danger  of 
death  from  choke-damp.  The  reason  is  simple.  When 
fire-damp,  or  marsh  gas,  explodes  with  air  the  carbon  is  con- 
verted into  choke-damp,  or  carbon  dioxide,  and  the  hydro- 
gen into  water.  Air  in  which  a  candle  will  not  burn  is 
not  fit  for  breathing  purposes. 

The  role  played  by  carbon  dioxide  in  nature  is  extremely 
important  and  interesting.  The  carbon  of  living  things  is 
obtained  from  carbon  dioxide,  and  returns  to  this  form  when 
life  ceases.  We  have  learned  that  all  living  things  contain 
carbon  as  an  essential  constituent.  Whence  comes  this  car- 
bon? Animals  eat  either  the  products  of  plant-life  or  other 
animals  which  derive  their  sustenance  from  the  vegetable 
kingdom.  The  food  of  animals  comes,  then,  either  directly 
or  indirectly  from  plants.  But  plants  derive  their  sustenance 
largely  from  the  carbon  dioxide  of  the  air.  The  plants  have 
the  power  to  decompose  the  gas  with  the  aid  of  the  direct 
light  of  the  sun,  and  they  then  build  up  the  complex  coin- 
pounds  of  carbon  which  form  their  tissues,  using  for  this  pur- 
pose the  carbon  of  the  carbon  dioxide  which  they  have  de- 
composed. Many  of  these  compounds  are  fit  for  food  for 
animals;  that  is  to  say,  they  are  of  such  composition  that  the 
forces  at  work  in  the  animal  body  are  capable  of  transform- 
ing them  into  animal  tissues,  or  of  oxidizing  them,  and 


188  INTRODUCTION  TO  CHEMISTRY. 

thus  keeping  the  temperature  of  the  body  up  to  the  neces- 
sary point.  That  part  of  the  food  which  undergoes  oxida- 
tion in  the  body  plays  the  same  part  as  fuel  in  a  stove.  It 
is  burned  up  with  an  evolution  of  heat,  the  carbon  being 
converted  into  carbon  dioxide,  which  is  given  off  from  the 
lungs.  From  fires  and  from  living  animals  carbon  dioxide 
is  returned  to  the  air,  where  it  again  serves  as  food  for  the 
plants.  When  the  life-process  stops  in  the  animal  or  plant, 
decomposition  begins;  and  the  final  result  of  this,  under 
ordinary  circumstances,  is  the  conversion  of  the  carbon 
into  carbon  dioxide. 

We  see,  thus,  that  under  the  influence  of  life  and  sun- 
light carbon  dioxide  is  converted  in  the  plant  into  com- 
pounds containing  carbon  which  are  stored  up  in  the  plant. 
These  compounds  are  capable  of  burning,  and  thus  giving 
heat;  or  some  of  them  may  be  used  as  food  for  animals,  as- 
suming still  more  complex  forms  under  the  influence  of  the 
life-process  of  the  animals.  As  long  as  life  con  tinues,  plants 
and  animals  are  storehouses  of  energy.  When  death  oc- 
curs, the  carbon  compounds  pass  back  to  the  form  of  carbon 
dioxide;  the  energy  which  was  stored  up  is  lost.  The 
power  to  do  work  which  the  carbon  compounds  of  plants 
and  animals  possess  comes  from  the  heat  of  the  sun.  It 
takes  a  certain  quantity  of  this  heat,  operating  under  proper 
conditions,  to  decompose  a.  certain  quantity  of  carbon  diox- 
ide and  elaborate  the  compounds  contained  in  the  plants. 
When  these  compounds  are  burned  they  give  out  the  heat 
which  was  used  up  in  their  formation  during  the  growth  of 
the  plants.  These  compounds  are  said  to  possess  chemical 
energy.  This  has  its  origin  in  heat,  and  is  capable  of  re- 
conversion into  heat.  The  transformation  of  the  energy  of 
the  sun's  heat  into  chemical  energy  lies  at  the  foundation 


CA11BONIC  A  CID.  189 

of  all  life.  As  the  heat  of  the  sun  acting  upon  the  great 
bodies  of  water  and  on  the  air  gives  rise  to  the  movements 
of  water  which  are  so  essential  to  the  existence  of  the  world 
as  it  is,  so  the  action  of  the  sun's  rays  on  carbon  dioxide,  in 
the  presence  of  the  delicate  and  inexplicable  mechanism  of 
the  leaf  of  the  plant,  gives  rise  to  those  changes  in  the  forms 
of  combination  of  the  element  carbon  which  accompany 
the  wonderful  process  of  life. 

Carbonic  Acid  and  Carbonates. — When  carbon  dioxide  is 
passed  into  water  the  solution  has  a  slightly  acid  reaction. 
[Try  it.]  The  solution  will  act  upon  basic  solutions  and 
form  salts.  The  formula  of  the  sodium  salt  formed  in  this 
way  has  been  shown  to  be  NaaC03;  that  of  the  potassium 
salt,  K2C03,  etc.  These  salts  are  plainly  derived  from  an 
acid,  H2C03,  which  is  carbonic  acid.  It  is  probable  that 
this  acid  is  contained  in  the  solution  of  carbon  dioxide  in 
water.  It  is,  however,  so  unstable  that  it  breaks  up  into 
carbon  dioxide  and  water  : 

H2C03  =  H20  -f  C02. 

When  carbon  dioxide  acts  upon  a  base  it  forms  a  salt. 
Thus,  with  potassium  hydroxide  or  calcium  hydroxide  the 
action  which  takes  place  is  represented  thus  : 

2KOH  +  C02  =  K2C08  -f  H20  ; 
CaO.H,  +  C02  =  CaC03  +  H20. 

With  the  acid  the  action  would  take  place  as  represented 
thus  : 

2KOH  +  H2003  =  K2C03  +  2H20  ; 
CaOaH3  +  H2C03  =  CaCO.  +  2HaO. 


190  INTRODUCTION  TO  CHEMISTRY. 

EXPERIMENT  93. — Pass  carbon  dioxide  into  a  solution  of 
caustic  potash  until  it  will  absorb  no  more.  Add  acid  to 
some  of  this  solution  and  convince  yourself  that  the  gas 
given  off  is  carbon  dioxide.  Write  the  equations  repre- 
senting the  reactions  which  take  place  on  passing  the  car- 
bon dioxide  into  the  caustic  potash  solution,  and  on  adding 
an  acid  to  the  solution.  Wnat  evidence  have  you  that  the 
gas  given  off  is  carbon  dioxide  ? 

EXPERIMENT  94. — Pass  carbon  dioxide  into  50  to  100  cc. 
clear  lime-water.  Filter  off  the  white  insoluble  substance. 
Try  the  action  of  a  little  acid  on  it.  What  evidence  have 
you  that  it  is  calcium  carbonate  ?  How  could  you  easily 
distinguish  between  lime-water  and  a  solution  of  caustic 
potash  ? 

Although,  as  we  have  seen,  when  carbon  dioxide  is 
passed  into  lime-water  calcium  carbonate  is  thrown  down, 
if  we  continue  to  pass  the  gas  for  some  time  the  calcium 
carbonate  dissolves,  and  finally  the  solution  becomes  clear. 
Water  alone  does  not  dissolve  calcium  carbonate,  but 
water  containing  carbon  dioxide  does.  If  this  solution  be 
heated,  the  carbon  dioxide  is  driven  off  and  the  calcium 
carbonate  is  again  thrown  down.  Natural  waters  whicli 
flow  over  lime-stone  take  up  more  or  less  calcium  carbonate 
by  virtue  of  the  carbon  dioxide  which  they  absorb  from 
the  air.  Such  waters  are  in  the  condition  of  the  solution 
of  calcium  carbonate  above  referred  to.  When  heated,  the 
calcium  carbonate  is  deposited.  This  is  frequently  noticed 
in  the  deposits  in  boilers  and  other  vessels  in  which  water 
is  boiled. 

EXPERIMENT  95.— Pass  carbon  dioxide  first  through  a  little 
water  to  wash  it,  and  then  into  50  to  100  cc/clear  lime-water. 
At  first  the  insoluble  carbonate  will  come  down,  as  in  Ex- 


CARBON  MONOXIDE.  191 

periment  94;  but  soon  it  will  begin  to  dissolve,  and  finally 
an  almost  clear  solution  will  be  obtained.  Heat  this  solu- 
tion, and  the  insoluble  carbonate  will  again  appear. 

Carbon  Monoxide,  CO. — When  a  substance  containing 
carbon  burns  in  an  insufficient  supply  of  air, — as,  for  ex- 
ample, when  the  draught  in  a  furnace  is  not  strong  enough 
to  remove  the  products  of  combustion  and  supply  fresh  air, 
— the  oxidation  of  the  carbon  is  not  complete,  and  the 
product,  instead  of  being  carbon  dioxide,  is  carbon  mon- 
oxide, CO.  This  substance  can  also  be  made  by  extract- 
ing oxygen  from  c.irbon  dioxide.  It  is  only  necessary  to 
pass  the  dioxide  over  heated  carbon,  when  reaction  takes 
place  as  represented  thus  : 

C02  +  0  =  200. 

This  method  of  formation  is  illustrated  in  coal  fires,  and 
can  be  well  observed  in  an  open  grate.  The  air  has  free 
access  to  the  coal,  and  at  the  surface  complete  oxidation 
takes  place.  But  that  part  of  the  carbon  dioxide  which  is 
formed  at  the  lower  part  of  4he  grate  is  drawn  up  through 
the  heated  coal  and  is  partly  reduced  to  carbon  monoxide. 
When  the  monoxide  escapes  from  the  upper  part  of  the 
grate  it  again  combines  with  oxygen,  or  burns,  giving  rise 
to  the  characteristic  blue  flame  always  noticed  above  a 
mass  of  burning  coal.  Should  anything  occur  to  prevent 
free  access  of  air,  carbon  monoxide  may  easily  escape  com- 
plete oxidation. 

It  is  also  formed  by  passing  water  over  highly  heated 
carbon,  when  this  reaction  takes  place  : 

0  +  H20  =  CO  +  2H. 
This  is  the  reaction  which  is  made  use  of  in  the  manu- 


192  INTRODUCTION  TO  CHEMISTRY. 

facture  of  "  water  gas."  The  gas  thus  obtained  is  a  mix- 
ture of  hydrogen  and  carbon  monoxide.  Before  use  it  is 
enriched  by  the  addition  of  hydrocarbons  from  petroleum. 
The  easiest  way  to  make  carbon  monoxide  is  to  heat 
oxalic  acid,  which  is  a  compound  of  carbon,  hydrogen,  and 
oxygen,  of  the  formula  C2H204,  with  five  to  six  times  its 
weight  of  concentrated  sulphuric  acid.  The  change  which 
takes  place  is  represented  thus  : 

C2H204  =  C0a  +  CO  +  H20. 

Both  carbon  dioxide  and  monoxide  are  formed.  Both 
are  gases.  In  order  to  separate  them  the  mixture  is  passed 
through  a  solution  of  caustic  soda,  which  takes  up  the 
carbon  dioxide  [forming  what  ?]  and  allows  the  monoxide 
to  pass. 

EXPERIMENT  96. — Put  ten  grams  crystallized  oxalic  acid 
and  50-60  grams  concentrated  sulphuric  acid  in  an  appro- 
priate-sized flask.  Connect  with  two  Wolff's  flasks  con- 
taining caustic-soda  solution.  Heat  the  contents  of  the 
flask  gently.  Collect  some  of  the  gas  over  water.  Set  fire 
to  some,  and  notice  the  characteristic  blue  flame.  Put  a 
live  mouse  in  a  vessel  containing  a  mixture  of  about  equal 
parts  of  carbon  monoxide  and  air.  It  will  die  unless  re- 
moved. 

Carbon  monoxide  is  a  colorless,  tasteless,  inodorous  gas, 
insoluble  in  water.  It  burns  with  a  pale  blue  flame, 
forming  carbon  dioxide.  It  is  exceedingly  poisonous  when 
inhaled,  Hence  it  is  very  important  that  it  should  not  be 
allowed  to  escape  into  rooms  occupied  by  human  beings. 
We  not  unf requently  hear  of  deaths  caused  by  the  gases  from 
coal  stoves.  The  most  dangerous  of  the  gases  given  off 
from  coal  stoves  is  carbon  monoxide,  A  pan  of  smoulder- 


FLAMES.  193 

ing  charcoal  gives  off  this  gas,  and  the  poisonous  character 
of  the  gas  is  well  known,  as  it  has  been  used  to  a  consider- 
able extent  for  the  purpose  of  suicide,  particularly  in 
France. 

At  high  temperatures  carbon  monoxide  has  a  very  strong 
affinity  for  oxygen,  and  is  hence  a  good  reducing  agent. 
In  the  reduction  of  iron  from  its  ores,  the  carbon  monox- 
ide formed  in  the  blast-furnace  plays  an  important  part  in 
the  reducing  process. 

EXPEEIMENT  97. — Pass  carbon  monoxide  over  some 
heated  copper  oxide  contained  in  a  hard  glass  tube.  Is 
the  oxide  reduced?  How  do  you  know?  Is  carbon  diox- 
ide formed?  What  evidence  have  you?  Was  the  carbon 
monoxide  used  free  of  carbon  dioxide?  If  not,  what  evi- 
dence have  you  that  carbon  dioxide  is  formed  in  this  ex- 
periment? 

Illumination,  Flame,  Blow-pipe,  etc. — As  the  substances 
used  for  illumination  contain  carbon,  and  the  chemical 
processes  involved  consist  largely  in  the  oxidation  of  the 
carbon  of  these  compounds,  this  is  an  appropriate  place  to 
consider  briefly  the  subject  of  illumination,  and  also  that 
of  flame,  and  the  blow-pipe,  which  is  an  extremely  useful 
form  of  flame  constantly  used  in  the  laboratory. 

In  all  ordinary  kinds  of  illumination  we  are  dependent 
upon  flames  for  the  light.  Whether  we  use  illuminating 
gas,  a  lamp,  or  a  candle,  the  light  comes  from  a  flame.  In 
the  first  case,  the  gas  is  burned  directly;  in  the  case  of  the 
lamp,  the  oil  is  first  drawn  up  the  wick,  then  converted 
into  a  gas,  and  this  burns;  while,  finally,  in  the  case  of 
the  candle,  the  solid  material  of  the  candle  is  first  melted, 
then  drawn  up  the  wick,  converted  into  gas,  and  the  gas 
burns,  forming  the  flame.  In  each  case  we  have,  then,  to 
13 


194  INTRODUCTION  TO  CHEMISTRY. 

deal  with  a  burning  gas,  and  this  burning  gas  we  call  a 
flame. 

Most  illuminating  gas  is  made  from  coal  by  heating  in 
closed  retorts.  As  has  already  been  explained,  coal,  particu- 
larly the  softer  kinds,  contains  compounds  of  carbon  and 
hydrogen,  together  with  some  nitrogen  and  other  ele- 
ments. When  it  is  heated  the  hydrogen  passes  off,  partly 
in  combination  with  carbon,  as  hydrocarbons,  and  partly 
in  the  free  state.  The  nitrogen  passes  off  as  ammonia, 
and  a  large  percentage  of  the  carbon  remains  behind  in  the 
retort  in  the  uncombined  state  as  coke.  The  gases  given 
off  are  purified,  and  form  ordinary  illuminating  gas.  One 
ton  of  coal  yields  on  an  average  10,000  cubic  feet  of  gas. 
The  value  of  a  gas  depends  upon  the  quantity  of  light 
given  by  the  burning  of  a  definite  quantity.  It  is  meas- 
ured by  comparing  it  with  the  light  given  by  a  candle 
burning  at  a  certain  rate.  The  standard  candle  is  one 
made  of  spermaceti,  which  burns  at  the  rate  of  120  grains 
per  hour;  that  is  to  say,  which,  burning  under  ordinary 
conditions,  loses  120  grains  in  one  hour.  The  standard 
burner  used  for  the  gas  is  one  through  which  5  cubic  feet 
of  gas  pass  per  hour.  Now,  if  we  wish  to  determine  the 
illuminating  power  of  a  gas,  we  pass  it  through  the 
standard  burner  at  the  rate  mentioned,  and  compare  the 
light  which  it  gives  with  the  light  given  by  the  standard 
candle.  The  comparison  is  easily  made  by  means  of  a  so- 
called  photometer.  The  illuminating  power  of  the  gas  is 
then  stated  in  terms  of  candles.  When  we  say  that  the 
illuminating  power  of  a  gas  is  fourteen  candles,  we  mean 
that,  when  burning  at  the  rate  of  5  cubic  feet  per  hour, 
its  flame  gives  fourteen  times  as  much  light  as  the  standard 
candle. 


FLAMES. 


195 


Ordinarily  when  we  speak  of  a  flame  we  mean  a  gas 
which  is  combining  with  oxygen.  The  hydrogen  flame  is 
simply  the  phenomenon  accompanying  the  act  of  combi- 
nation of  the  two  gases  hydrogen  and  oxygen.  Owing  to 
the  fact  that  we  are  surrounded  by  oxygen,  we  speak  of 
hydrogen  as  the  burning  gas.  How  would  it  be  if  we 
were  surrounded  by  an  atmosphere  of  hydrogen?  Plainly, 
oxygen  would  then  be  a  burning  gas.  If  we  cause  a  jet  of 
oxygen  to  escape  into  a  vessel  containing  hydrogen,  a 
flame  will  appear  where  the  oxygen  escapes  from  the  jet,  if 
a  light  be  applied.  This  is  an  experiment  which  requires 
great  precautions,  and,  as  the  principle  can  be  illustrated 
as  well  by  means  of  illuminating  gas,  we  may  use  this  in- 
stead. Just  as  illuminating  gas  burns  in  an  atmosphere  of 
oxygen,  so  oxygen  burns  in  an  atmosphere  of  illuminating 
gas. 

EXPEEIMENT  98.— Break  off  the  neck  of  a  good-sized  re- 


FIG.  40. 


Lort ;  fit  a  perforated  cork  to  the  small  end;  pass  a  piece 
of  glass  tube  through  the  cork  and  connect  by  means  of 
rubber  hose  with  an  outlet  for  gas.  Fix  the  apparatus  in 


196  INTRODUCTION  TO  CHEMISTRY. 

position,  as  shown  in  Fig.  40.  Turn  the  gas  on,  and 
when  the  air  is  driven  out  of  the  retort-neck,  light  the  gas. 
You  now  have  the  neck  filled  with  illuminating  gas,  and 
the  gas  is  burning  at  the  mouth  of  the  vessel.  If  now  a 
platinum  jet  from  which  oxygen  is  issuing  be  passed  up 
into  the  gas  the  oxygen  will  take  fire,  and  a  flame  will  ap- 
pear where  the  oxygen  escapes  from  the  jet.  The  oxygen 
burns  in  the  atmosphere  of  coal  gas. 

In  considering  the  action  of  oxygen  upon  other  sub- 
stances, we  learned  that  it  is  necessary  that  each  of  these 
substances  should  be  raised  to  a  certain  temperature  before 
it  will  combine  with  the  oxygen.  This  statement  is  as  true 
of  gases  as  of  other  substances.  When  a  current  of  hydro- 
gen is  allowed  to  escape  into  the  air,  or  into  oxygen,  no 
action  takes  place  unless  it  be  heated  up  to  its  burning 
temperature,  when  it  takes  fire  and  continues  to  burn,  as 
the  burning  of  one  part  of  the  gas  heats  up  the  part  which 
follows  it,  and  hence  the  gas  is  heated  up  to  the  burning 
temperature  as  fast  as  it  escapes  into  the  air.  If  the  gas 
should  be  cooled  down  even  very  slightly  below  this  tem- 
perature, it  would  be  extinguished.  This  is  shown  .in  a 
very  striking  manner  by  the  following  experiments : 

EXPERIMENT  99. — Light  a  Bunsen  burner.  Bring  down 
upon  the  flame  a  piece  of  brass  or  iron  wire  gauze. 
There  is  no  flame  above  the  gauze.  That  the  gas  passes 
through  unburned  can  be  shown  by  applying  a  light  just 
above  the  outlet  of  the  burner  and  above  the  gauze.  The 
gas  will  take  fire  and  burn.  By  simply  passing  through 
the  thin  wire  gauze,  then,  the  gas  is  cooled  down  below  its 
burning  temperature,  and  does  not  burn  unless  it  is  heated 
up  again.  Turn  on  a  Bunsen  burner.  Do  not  light  the 
gas.  Hold  a  piece  of  wire  gauze  about  one  and  a  half  to 


SAFETY-LAMP. 


197 


two  inches  above  the  outlet.  Apply  a  lighted  match  above 
the  gauze,  when  the'gas  will  burn  above  the  gauze,  but  not 
below  it.  Here  again  the  heat  necessary  to  raise  the  tem- 
perature of  the  gas  to  the  burning  temperature  cannot  be 
communicated  through  the  gauze.  If  in  either  of  the 
above-described  experiments  the  gauze  be  held  in  position 
for  a  time,  it  will  probably  become  so  highly  heated  that 
the  gas  on  the  side  where  there  is  no  flame  will  be  raised  to 
the  burning  temperature.  The  instant  that  point  is 
reached  the  flame  becomes  continuous. 

The  principle  illustrated  in  the  preceding  experiments 
is  utilized  in  the  miner's  safety-lamp,  to  which  reference 
has  already  been  made.  One  of  the  dangers  which  the 
coal-miner  has  to  encounter  is  the  occur- 
rence of  fire-damp,  or  methane,  CH4,  which 
with  air  forms  an  explosive  mixture.  The 
explosion  can  only  be  brought  about  by 
contact  of  flame  with  the  mixture.  Li 
order  to  avoid  the  contact,  the  flame 
of  the  safety-lamp  is  surrounded  by 
wire  gauze,  as  shown  in  Fig.  41. 
When  a  lamp  of  this  kind  is  brought 
into  an  explosive  mixture  of  marsh  gas 
and  air,  what  takes  place?  The  mixture 
passes  through  the  wire  gauze  and  comes 
in  contact  with  the  flame,  a  small  explo- 
sion inside  the  gauze  occurs,  but  the  flame 
of  the  burning  gas  inside  the  wire  gauze 
cannot  pass  through  and  raise  the  tem- 
perature of  the  gas  outside  to  the  burning 
temperature.  Hence  no  serious  explosion  FIG.  41. 

can   take   place.      The   flickering   of    the    flame    of    the 


198  INTRODUCTION  TO  CHEMISTRY. 

lamp,  and  the  occurrence  of  small  explosions  inside,  fur- 
nish the  miner  with  the  information  that  he  is  in  a  dan- 
gerous atmosphere. 

Structure  of  Flames.  —  The  hydrogen  flame  consists 
of  a  thin  envelope  of  burning  hydrogen  enclosing  un- 
burned  gas,  and  surrounded  by  water  vapor,  which  is  the 
product  of  the  combustion.  The  structure  of  other 
flames  depends  upon  the  complexity  of  the  gases  burned 
and  the  conditions  under  which  the  burning  takes  place. 
In  general,  a  flame  consists  of  an  outer  envelope  of  gas 
combining  with  oxygen,  and  hence  hot,  and  an  inner  part 
which  contains  unburned  gas,  which  is,  for  the  most  part, 
cool.  A  part  of  the  unburned  gas  is,  however,  hot,  and  it 
would  combine  with  oxygen  were  it  not  for  the  fact  that  it 
is  surrounded  by  an  envelope  which  prevents  access  of  air. 
The  outer  hot  part  of  the  flame  is  called  the  oxidizing  flame, 
because  it  presents  conditions  favorable  to  the  oxidation  of 
substances  introduced  into  it.  The  inner  hot  part  is  called 
the  reducing  flame,  because  it  consists  of  highly  heated 
substances  which  have  the  power  to  combine  with  oxygen, 
and  hence  many  compounds  containing  oxygen  lose  it,  or 
are  reduced,  when  introduced  into  this  part  of  the  flame. 
The  hottest  part  of  the  flame  is  at  the  extreme  top.  Here 
oxidation  is  taking  place  most  energetically.  The  hottest 
part  of  the  unburned  gases  is  at  the  tip  of  the  dark  central 
part  of  the  flame.  In  the  flame  of  a  Bunsen  burner  the 
two  parts  can  be  distinguished  very  easily.  The  dark  cen- 
tral part  of  the  flame  extends  for  some  distance  above  the 
outlet  of  the  burner.  If  the  holes  at  the  base  of  the  burner 
be  partly  closed,  the  tip  of  the  central  part  of  the  flame  be- 
comes luminous.  This  luminous  tip  is  most  efficient  for 
the  purpose  of  reduction.  The  principal  parts  of  the  flame 


BLOW- PI  PR  199 

are  those  marked  in  Fig.  42.  B  is  the  central  cone  of  un- 
burned  gas.  G  is  the  luminous  tip,  the  best  part 
of  the  flame  for  reduction.  A  is  the  envelope  of 
burning  gas.  This  is  further  surrounded  by  a 
non-luminous  envelope  consisting  of  the  products 
of  combustion,  carbon  dioxide  and  water  vapor. 
Certain  metals  placed  in  the  upper  end  of  the 
flame  take  up  oxygen,  because  they  are  highly 
heated  in  the  presence  of  oxygen.  Certain  oxides 
lose  their  oxygen  when  placed  in  the  tip  of  the 
central  cone,  because  the  gases  are  here  heated  to 
the  temperature  at  which  they  have  the  power  to 
combine  with  oxygen.  FIG.  42. 

The  oxidizing  and  reducing  flumes  are  frequently  util- 
ized in  the  laboratory.  For  the  purpose  of  increasing  their 
efficiency  a  Uow-pipe  is  used.  This  is  a  tube  through  which 
air  is  blown  by  means  of  the  mouth  into  a  flame.  It  is 
usually  constructed  in  the  shape  shown  in  Fig.  43.  At  the 

bgg  smaller  end,  which  is  placed  in  the 
|  flame,  there  is  usually  a  small  tube  of 
FIG.  43.  platinum.      The  blow-pipe  may  be 

used  with  the  flame  of  a  candle,  an  alcohol-lamp,  or  a  gas- 
lamp.  It  is  most  frequently  used  with  the  gas-lamp.  A 
piece  of  brass  tubing  which  fits  snugly  in  the  tube  of  a 
Bunsen  burner  is  cut  off  and  hammered  together  so  as  to 
leave  a  narrow  slit-like  opening.  This  tube  is  then  slipped 
into  the  burner,  as  shown  in  Fig.  44.  It  reaches  to  the 
bottom  of  the  burner,  and  thus  cuts  off  the  supply  of 
air  which  usually  enters  the  holes  at  the  base.  The  gas 
is  now  lighted  and  the  current  so  regulated  that  there 
is  a  small  flame  about  1£  to  2  inches  high.  The  tip 
of  the  blow-pipe  is  placed  on  the  slit  of  the  burner  in 


200 


INTRODUCTION  TO  CHEMISTRY. 


the  flame,  so  that  it  extends  about  one  third  the  way  across 
it,  as  shown  in  Fig.  45.  By  blowing  regularly  and  not 
too  violently  through  the  pipe  the  flame  is  forced  down 
in  the  same  direction  as  the  end-piece  of  the  blow-pipe,  and 
the  slant  of  the  burner  slit.  Under  proper  conditions  it 
separates  sharply  into  a  central  blue  part  and 
an  outer  part  of  another  color.  The  direc- 
tion and  lines  of  division  of  the  flame  are 


FIG.  44. 


FIG.  45. 


FIG.  46. 


indicated  in  Fig.  46.  The  extreme  outer  tip  A  is  the 
most  efficient  oxidizing  flame.  The  tip  B  of  the  inner 
blue  part  is  the  most  efficient  reducing  flame. 

The  use  of  the  blow-pipe  is  illustrated  by  the  following 
experiments: 

EXPERIMENT  100. — Select  a  piece  of  charcoal  about  4 
inches  long  by  1  inch  wide  and  1  inch  thick,  with  one  sur- 
face plane.*  Near  the  end  of  the  plane  surface  make  a 
cavity  by  pressing  the  edge  of  a  cent  piece  or  similar  coin 
against  it,  and  turning  it  completely  round  a  few  times. 
Mix  together  equal  small  quantities  of  dry  sodium  carbon- 
ate and  lead  oxide.  Put  a  little  of  the  mixture  in  the 
cavity  in  the  charcoal,  and  heat  it  in  the  reducing  flame 
produced  by  the  blow-pipe.  In  a  short  time  globules  of 

*  Pieces  of  charcoal  prepared  for  blow-pipe  work  can  be  bought 
from  dealers  in  chemical  apparatus  at  small  cost. 


BLOW-PIPE  EXPERIMENTS.  201 

metallic  lead  will  be  seen  in  the  molten  mass.  After  cool- 
ing,  scrape  the  solidified  substance  out  of  the  cavity  in  the 
charcoal.  Put  it  in  a  small  mortar,  treat  it  with  a  little 
water,  and,  after  breaking  it  np  and  allowing  as  much  as 
possible  to  dissolve,  pick  out  the  metallic  beads.  [Is  it 
malleable  or  brittle  ?  Is  metallic  lead  malleable  or  brittle? 
Is  it  dissolved  by  hydrochloric  acid  ?  Is  lead  soluble  in 
hydrochloric  acid  ?  Is  it  soluble  in  nitric  acid  ?  Is  lead 
soluble  in  nitric  acid  ?]  The  action  of  the  acids  may  be 
tried  by  putting  the  bead  on  a  small  dry  watch-glass  and 
adding  a  few  drops  of  the  acid.  [Does  the  substance  act 
like  lead?  What  has  become  of  the  oxygen  with  which  the 
lead  was  combined  in  the  oxide?  Is  there  any  special  ad- 
vantage iu  having  a  support  of  charcoal  for  this  experi- 
ment ?] 

EXPERIMENT  101. — Heat  a  small  piece  of  metallic  lead 
on  charcoal  in  the  oxidizing  blow-pipe  flame.  Notice  the 
formation  of  the  oxide,  which  forms  a  coating  or  film  on  the 
charcoal  in  the  neighborhood  of  the  metal.  [Is  there  any 
analogy  between  this  process  and  the  burning  of  hydrogen? 
In  what  does  the  analogy  consist?  What  differences  are 
there  between  the  two  processes?] 

Some  oxides  are  reduced  very  easily  when  heated  in  the 
reducing  blow-pipe  flame.  Others  are  not.  We  are  fre- 
quently able  to  judge  of  the  composition  of  a  substance  by 
heating  it  in  the  blow-pipe  flame  and  noticing  its  conduct. 
Some  metals  are  easily  oxidized  in  the  oxidizing  flame. 
Some  form  characteristic  films  of  oxides  on  the  charcoal, 
and  in  some  cases  it  is  possible  to  detect  the  presence  of 
certain  substances  by  noticing  the  color  of  the  film  of  ox- 
ide. The  blow-pipe  is  therefore  of  great  value  as  affording 
a  means  of  detecting  the  presence  of  certain  elements  in 


202  INTRODUCTION  TO  CHEMISTRY. 

mixtures  or  compounds  of  unknown  composition.  The 
chemical  principles  involved  in  its  use  will  be  clear  from 
what  has  already  been  said. 

Causes  of  the  Luminosity  of  Flames. — It  is  evident  from 
what  we  have  seen  that  flames  vary  greatly  in  their  light- 
giving  power.  The  hydrogen  flume,  for  example,  gives 
practically  no  light.  This  is  also  the  case  with  the  flame 
of  the  Bunsen  burner;  while,  on  the  other  hand,  the 
flame  of  illuminating  gas  burning  under  ordinary  circum- 
stances, and  of  a  candle,  etc.,  give  light.  What  is  the  dif- 
ference due  to  ?  There  are  several  causes  which  operate  to 
make  a  flame  give  light,  and  vice  versa.  In  the  first  place, 
if  a  solid  substance  which  does  not  burn  up  is  introduced 
into  a  non-luminous  flame,  a  part  of  the  heat  appears  as 
light.  This  is  seen  when  a  spiral  of  platinum  wire  is  in- 
troduced into  a  hydrogen  flame.  It  has  also  been  shown 
by  introducing  a  piece  of  lime  into  the  hot  non-luminous 
flame  of  the  oxyhydrogen  blow-pipe.  A  similar  cause 
operates  in  ordinary  gas  flames  to  make  them  luminous. 
There  are  always  present  particles  of  unburned  carbon,  as 
can  be  shown  by  putting  a  piece  of  porcelain  or  any  solid 
substance  into  the  flame,  when  there  will  be  deposited  in  it 
a  layer  of  soot,  which  consists  mainly  of  finely  divided  car- 
bon. In  the  flame  these  particles  of  carbon  are  heated  to 
the  temperature  at  which  they  give  light.  Again,  it  has 
been  found  that  the  same  candle  gives  more  light  at  the 
level  of  the  sea  than  it  does  when  at  the  top  of  a  high  moun- 
tain, as  Mont  Blanc,  on  which  the  experiment  was  actually 
performed.  This  is  partly  due  to  a  difference  in  the  density 
of  the  gases.  Naturally,  the  denser  the  gas  the  more  active 
the  combustion,  the  greater  the  heat,  and  the  greater  the 
light.  This  last  statement  ceases  to  be  true  when  the  oxi- 


LVMINOSIVY  OF  FLAMES.  203 

dation  becomes  sufficient  to  burn  up  all  the  solid  particles 
of  carbon  in  the  flame.  If  gases  which  in  burning  give  light 
are  cooled  down  before  they  are  burned,  the  luminosity  is 
diminished,  arid,  conversely,  non-luminous  flames  may  be 
rendered  luminous  by  heating  the  gases  before  burning 
them. 

Gases  which  give  luminous  flames  give  non-luminous 
flames  when  diluted  to  a  sufficient  extent  with  neutral 
gases,  such  as  nitrogen  and  carbon  dioxide,  which  neither 
burn  nor  support  combustion. 

All  the  statements  made  in  regard  to  the  causes  of  the 
•luminosity  of  flames  are  based  upon  carefully  performed  ex- 
periments. These  experiments,  however,  cannot  readily 
be  repeated  by  the  student  in  the  laboratory  in  a  satisfac- 
tory way.  One  constant  reminder  of  the  possibility  of 
rendering  aluminous  flame  non-luminous,  and  vice  versa,  is 
furnished  by  the  burner  universally  used  in  chemical  labo- 
ratories, and  called,  after  the  name  of  its  inventor,  the 
Bunsen  burner.  The  construction  of  this  burner  is  easily 
understood.  It  consists  of  a  base  and  an  upper  tube. 
The  base  is  connected  by  means  of  a  rubber  tube  with  the 
gas  supply.  The  gas  escapes  from  a  small  opening  in  the 
base,  and  passes  up  through  the  tube.  At  the  lower  part 
of  the  tube  there  are  two  holes,  which  may  be  opened  or 
closed  by  turning  a  ring  with  two  corresponding  holes  in  it. 
When  the  gas  is  turned  on,  it  is  lighted  at  the  top  of  the 
tube.  Air  is  at  the  same  time  drawn  through  the  holes  at 
the  base.  The  result  is  that  the  flame  is  practically  non- 
luminous.  If  the  ring  at  the  base'  be  turned  so  that  the 
air-holes  are  closed,  the  flame  becomes  luminous.  The  ad- 
vantage of  the  non-luminous  flame  for  laboratory  use  con- 


204  INTRODUCTION  TO  CHEMISTRY. 

sists  in  the  fact  that  it  does  not  deposit  soot,  and,  at  the 
same  time,  gives  a  good  heat. 

[Could  the  hydrogen  flame  deposit  soot?] 

The  non-luminosity  of  the  flame  of  the  Bunsen  burner 
appears  to  be  due  to  several  causes  :  (1)  Dilution  of  the 
gases  by  means  of  the  nitrogen  of  the  air;  (2)  Cooling  of 
the  gases  by  the  entrance  of  the  air;  (3)  Burning  of  the 
solid  particles  by  the  aid  of  the  oxygen  of  the  air  admitted 
•  to  the  interior  of  the  flame. 

Cyanogen,  C2N"2. — Carbon  does  not  combine  with  nitro- 
gen under  ordinary  circumstances.  If,  however,  they  are 
brought  together  at  very  high  temperatures  in  the  pres- 
ence of  metals,  they  combine  to  form  compounds  known 
as  cyanides.  Thus,  when  nitrogen  is  passed  over  a  highly 
heated  mixture  of  carbon  and  potassium  carbonate,  K2C03, 
the  compound  potassium  cyanide,  KCN,  is  formed.  Car- 
bon containing  nitrogen,  as  animal  charcoal,  when  ignited 
with  potassium  carbonate,  reduces  the  potassium  carbonate, 
forming  potassium,  which  causes  the  carbon  and  nitrogen 
to  combine,  forming  potassium  cyanide.  When  refuse 
animal  substances,  such  as  blood,  horns,  claws,  hair,  wool, 
etc.,  are  heated  together  with  potassium  carbonate  and 
iron,  a  substance  known  as  potassium  ferrocyanide,  or 
yellow  prussiate  of  potash,  4KCN.Ee(CN)a  +  3HaO,  is 
formed.  When  this  is  simply  heated  it  decomposes, 
yielding  potassium  cyanide.  It  is  not  a  difficult  matter 
to  make  mercury  cyanide,  Hg(CN)2,  from  the  potassium 
compound.  By  heating  mercury  cyanide  it  breaks  up, 
yielding  metallic  mercury  and  cyanogen  gas: 
Hg  (CN),  =  Hg  +  0  A- 

[What  analogy  is  there  between  this  reaction  and  that 
which  takes  place  when  mercury  oxide  is  heated?] 


HYDROCYANIC  ACID.  205 

Cyanogen  is  a  colorless  gas.  Ifc  receives  its  name  from 
the  fact  that  many  of  its  compounds  are  blue  (nvavos, 
Hue).  It  is  easily  soluble  in  water  and  "alcohol.  It  is 
extremely  poisonous. 

Hydrocyanic  Acid,  Prussic  Acid,  HON. — This  acid  oc- 
curs in  nature  in  combination  with  other  substances, — in- 
bitter  almonds,  the  leaves  of  the  cherry,  laurel,  etc.  It 
is  prepared  by  treating  compounds  of  the  metals  and 
cyanogen  with  strong  acids.  Thus,  by  treating  potassium 
cyanide  with  sulphuric  acid  this  reaction  takes  place: 

2KCN  +  H2S04  =  K2S04  +  2HCN. 

[Which  reactions  already  considered  does  this  suggest?] 
Further,  by  treating  potassium  cyanide  with  hydrochloric 
acid,  hydrocyanic  acid  is  liberated: 

KCN  +  HC1  =  KC1  +  HON. 

[Which  is  the  stronger  acid,  hydrochloric  or  hydrocyanic 
acid?  Is  sulphuric  acid  stronger  than  hydrochloric  acid? 
Is  it  stronger  than  hydrocyanic  acid?] 

Hydrocyanic  acid  is  a  volatile  liquid  which  boils  at  26.5°, 
and  solidifies  at  —15°.  It  has  a  very  characteristic  odor 
resembling  that  of  bitter  almonds.  It  is  extremely  poi- 
sonous. It  dissolves  in  water  in  all  proportions,  and  it  is 
such  a  solution  which  is  known  as  prussic  acid. 

Both  cyanogen  and  hydrocyanic  acid  are  extremely  un- 
stable. In  the  presence  of  water,  the  nitrogen  tends  to 
combine  with  hydrogen  to  form  ammonia,  and  the  carbon 
with  oxygen  and  hydrogen  to  form  more  stable  compounds. 

Summary. — Carbon  is  contained  in  all  living  things,  and 
in  their  fossil  remains.  The  number  of  compounds  which 


206  INTRODUCTION  TO  CHEMISTRY. 

it  forms  is  almost  infinite.  They  are  usually  considered 
together  under  the  head  of  Organic  Chemistry. 

Carbon  is  found  in  the  atmosphere  in  the  form  of  car- 
bon dioxide,  and  in  the  form  of  carbonates,  widely  dis- 
tributed in  the  earth. 

Uncombined,  it  occurs  in  nature  as  diamond  and 
graphite. 

Amorphous  carbon  is  a  third  variety  of  carbon.  Char- 
coal in  its  various  forms  is  amorphous  carbon.  It  is  made  by 
charring  organic  substances  which  contain  carbon,  hydro- 
gen, and  oxygen.  Coke,  lamp-black,  and  bone-black  are 
other  forms  of  amorphous  carbon.  Bone-black  has  the 
power  to  extract  coloring  matters  from  solutions.  Charcoal 
has  the  power  to  absorb  gases,  and  is  used  for  purifying 
air.  It  also  absorbs  disagreeable  substances  from  water, 
and  is  used  for  the  purpose  of  purifying  water. 

Coal  is  a  form  of  carbon  found  in  nature  in  many  va- 
rieties. The  soft  coals  contain  more  hydrogen  than  the 
hard  coals,  which  contain  a  larger  percentage  of  carbon. 

At  ordinary  temperatures  carbon  is  a  very  inactive  ele- 
ment. At  high  temperatures  it  combines  with  oxygen 
with  avidity.  It  is  hence  a  good  reducing  agent,  and  is 
ased  extensively  as  such  in  the  extraction  of  metals  from 
their  ores. 

Carbon  forms  a  large  number  of  compounds  with  hydro- 
gen. These  are  the  hydrocarbons.  Many  of  these  are 
found  in  nature,  as  in  petroleum,  which  is  a  complex 
mixture  of  hydrocarbons.  Most  of  those  which  occur  in 
petroleum  belong  to  a  series  the  members  of  which  are 
closely  related  to  one  another.  In  composition  they  differ 
by  CHa,  or  a  multiple  of  this.  The  series  begins  with 
marsh  gas  and  is  known  as  the  marsh -gas  series.  A  series 


SUMMARY.  207 

of  this  kind  is  known  as  an  homologous  series.  There  are 
several  other  homologous  series  of  hydrocarbons.  This 
kind  of  relation  is  characteristic  of  carbon  compounds. 
Marsh  gas  is  found  in  nature  wherever  organic  matter 
undergoes  decomposition  without  free  access  of  air,  as  under 
water.  It  is  found  in  coal-mines,  and  is  a  source  of  danger, 
as  with  air  it  forms  an  explosive  mixture. 

Carbon  dioxide  is  formed  in  many  natural  processes,  as 
in  respiration,  combustion,  decay,  and  fermentation.  It  is 
prepared  by  treating  a  carbonate  with  an  acid.  The  gas 
given  off  is  not  the  acid,  but  a  substance  which  bears  to  the 
acid  the  relation  of  an  anhydride. 

Carbon  dioxide  is  the  food  of  plants.  Plants  form  the 
food  of  animals.  Animals  give  back  carbon  dioxide  to  the 
air  in  the  process  of  breathing.  After  death  the  carbon 
of  animals  and  plants,  if  left  exposed  to  the  air,  passes  back 
to  the  form  of  carbon  dioxide,  and  again  starts  on  its  round. 

Carbon  dioxide  forms  salts,  with  bases.  These  have  the 
general  formula  M2C03,  in  which  M  represents  any  metal, 
such  as  potassium,  sodium,  etc.  These  are  very  unstable, 
being  decomposed  by  any  acid.  Carbonic  acid  is  the  weakest 
of  all  acids. 

Calcium  carbonate  is  insoluble  in  water,  but  it  dissolves 
in  water  containing  carbon  dioxide.  When  heated  the 
carbon  dioxide  is  driven  off  and  the  calcium  carbonate 
deposited.  This  phenomenon  is  the  same  as  that  which 
gives  rise  to  the  ordinary  boiler  incrustations. 

Carbon  monoxide  is  a  poisonous  gas,  which  is  formed 
by  incomplete  oxidation  of  carbon  or  incomplete  reduction 
of  carbon  dioxide.  It  is  formed  in  ordinary  coal  fires  by 
the  passage  of  carbon  dioxide  over  thoroughly  heated  coal. 


208  INTRODUCTION  TO  CHEMISTRY. 

It  has  strong  affinity  for  oxygen,  and  is  hence  a  good  re- 
ducing agent. 

A  flame  is  a  burning  gas.  A  gas  which  burns  in  oxygen 
will  form  an  atmosphere  in  which  oxygen  will  burn.  If  a 
burning  gas  be  cooled  down  even  very  slightly  below  its 
burning  temperature,  it  is  extinguished.  The  miner's 
safety-lamp  consists  of  a  flame  surrounded  by  a  piece  of 
wire  gauze.  The  gas  cannot  pass  through  this  gauze  with- 
out being  cooled  down  below  the  burning  temperature. 

Flames  are  made  up  of  different  parts  with  different 
properties.  The  outer  tip  is  the  hottest  part,  and  is  called 
the  oxidizing  flame.  The  tip  of  the  dark  inner  part,  con- 
sisting of  unburned  gas,  is  the  reducing  flame. 

A  luminous  flame  can  be  made  non-luminous  by  diluting 
the  burning  gas  with  neutral  gases;  by  cooling  the  gases; 
by  introducing  oxygen  into  the  gas  so  as  to  effect  complete 
oxidation  of  the  carbon. 

In  the  presence  of  metals  carbon  and  nitrogen  combine 
to  form  cyanides.  From  these,  cyanogen  and  hydrocyanic 
acid  are  obtained. 


CHAPTEE  XI. 

THEORY  IN  REGARD  TO  THE  CAUSE  OF  THE  LAWS 
OF  DEFINITE  AND  MULTIPLE  PROPORTIONS.— 
ATOMIC  THEORY.— ATOMIC  WEIGHTS.— MOLECULAR 
WEIGHTS.— MOLECULAR  FORMULAS. 

ONE  of  the  most  characteristic  facts  observed  in  chemical 
action  is  that  it  takes  place  between  definite  weights  of 
substances.  This  subject  has  already  been  discussed,  and  it 
has  been  pointed  out  that,  as  the  result  of  the  examination 
of  a  large  number  of  cases,  it  has  been  discovered  that  these 
two  laws  always  hold  good: 

1.  Chemical  combination  always  takes  place  between 
definite  masses  of  substances. 

2.  If  two  elements,  A  and  B,  combine  in  different  pro- 
portions, the  relative  quantities  of  B  which  combine  with 
any  fixed  quantity  of  A  bear  a  simple  ratio  to  one  an- 
other. 

These  are  the  laws  of  definite  and  multiple  proportions. 
They  are  simply  condensed  statements  which  sum  up  what 
has  been  found  to  be  true  in  all  cases  examined.  They 
are  statements  of  facts  discovered  by  actual  experiment. 

It  is,  however,  one  thing  to  know  a  general  fact,  and 
quite  another  to  know  the  cause  of  the  fact.  We  know 
that  all  bodies  are  attract^  by  the  earth,  and  that  they 
fall  when  thrown  in  the  fr.  This  is  a  very  remarkable 
fact,  and  one  of  immeiree  importance.  We  know  that  it 
is  true,  as  we  have  evidence  of  its  truth  every  day.  But 
U 


210  INTRODUCTION  TO  CHEMISTRY. 

yet  we  do  not  know  why  it  is  so.  We  say  that  the  earth 
attracts  other  bodies  by  virtue  of  gravitation,  but  this  does 
not  tell  us  anything  whatever  about  the  cause  of  the  phe- 
nomenon. We  might  verify  the  law  of  universal  attrac- 
tion over  and  over  again  without  getting  any  nearer  to  the 
explanation.  So,  too,  we  might  verify  the  important  laws 
of  definite  and  multiple  proportions  over  and  over  again 
without  being  able  to  give  an  answer  to  the  question,  Why 
do  substances  combine  according  to  these  laws? 

When  we  have  established  a  law  by  means  of  experi- 
ments, and  have  accomplished  all  we  can  by  means  of  ex- 
periments, the  next  thing  in  order  is  to  imagine  a  cause. 
We  try  to  imagine  a  condition  of  things  which,  if  it  ex- 
isted, would  lead  to  the  results  discovered.  If  we  succeed 
in  imagining  such  condition  of  things,  we  suggest  an  hypoth- 
esis. If,  now,  we  test  this  hypothesis  in  every  way  that 
suggests  itself,  and  find  that  all  facts  discovered  are  in  ac- 
cordance with  it,  we  then  call  it  a  theory.  An  hypothesis 
is  a  guess  in  regard  to  the  cause  of  certain  phenomena.  A 
theory  is  an  hypothesis  which  has  been  thoroughly  tested, 
and  which  is  applicable  to  a  large  number  of  related  phe- 
nomena. 

Hypotheses  and  theories  are  of  great  value  to  science,  if 
founded  upon  a  thorough  knowledge  of  the  facts  to  which 
they  relate.  They  become  dangerous  when  used  by  those 
who  are  not  familiar  with  the  facts.  Those  whose  minds 
have  not  been  properly  trained  are  apt  to  be  given  to  un- 
profitable speculation.  The  student  who  has  not  received 
a  thorough  scientific  training  should  remember  that  theories 
and  hypotheses,  to  be  of  value,  must  be  suggested,  not  by 
a  superficial  but  by  a  thorough  knowledge  of  facts. 

With  these  words  of  warning  and  of  explanation  in  re- 


ATOMIC  THEORY.  211 

gard  to  the  relation  existing  between  the  fact,  the  law,  the 
hypothesis,  and  the  theory,  we  may  proceed  to  consider 
briefly  a  theory  concerning  the  constitution  of  matter 
which  grew  out  of  the  discovery  of  the  law,s  of  definite 
and  multiple  proportions. 

The  Atomic  Theory,  — If  we  consider  any  simple  form  of 
matter  or  element,  such  as  iron,  it  is  clear  that  there  are 
two  views  which  we  may  hold  regarding  the  way  the  sub- 
stance is  made  up.  We  know  we  can  subdivide  every 
piece  of  iron  we  can  see,  no  matter  how  small  it  may  be; 
and  though  after  a  time  the  particles  might  become  so 
small  that  we  could  no  longer  subdivide  them,  still  we  can 
imagine  that  by  more  refined  methods  the  process  of  sub- 
division might  be  continued  indefinitely.  If  we  believe 
that  such  infinite  subdivision  is  possible,  we  hold  the  hy- 
pothesis that  matter  is  infinitely  divisible.  We  cannot 
prove  this — we  must  speculate  in  regard  to  it.  But  we 
may  also  conceive  that  after  the  process  of  subdivision  has 
been  carried  on  for  a  time  until  very  minute  particles  have 
been  reached,  a  limit  would  be  found  beyond  which  the 
process  of  subdivision  could  not  be  carried.  If  we  believe 
this,  we  hold  the  hypothesis  that  matter  is  not  infinitely 
divisible,  and  this  carries  with  it  the  belief  that  matter 
consists  of  indivisible  particles.  These  particles  may  be 
called  atoms  (from  the  Greek  arojuoz,  which  signifies 
simply  indivisible).  Both  of  these  hypotheses  have  been 
held  for  ages.  But  the  discussion  in  regard  to  the  relative 
merits  of  the  two  views  was  not  much  more  profitable 
than  it  would  be  if  carried  on  between  two  students  who 
are  in  the  early  stages  of  their  study  of  the  facts. 

When  the  laws  of  definite  and  multiple  proportions  were 
discovered  l^y  the  English  chemist  Dalton,  in  the  early 


212  INTRODUCTION  TO  CHEMISTRY. 

part  of  the  present  century,  he  saw  that  the  conception 
that  matter  is  made  up  of  indivisible  particles  or  atoms 
might  have  some  connection  with  the  laws.  If  each  ele- 
ment is  made  up  of  atoms,  the  most  probable  view  is  that 
every  atom  of  any  particular  element  is  exactly  like  every 
other  atom  of  that  element.  Among  the  properties 
possessed  by  these  atoms  must  be  weight.  It  is  probable 
that  the  atoms  of  different  elements  have  different  weights. 
Suppose  now  that,  when  chemical  combination  takes  place 
between  two  elements,  the  real  action  takes  place  between 
these  atoms,  so  that  one  atom  of  the  one  element  com- 
bines with  one  of  the  other,  and  so  on  through  the 
mass.  If  there  were  present  in  one  mass  exactly  as  many 
atoms  as  in  the  other,  both  substances  would  be  used  up — 
nothing  would  be  left  over.  But  if  there  were  a  larger 
number  of  atoms  of  one  element  than  of  the  other,  then, 
of  the  element  of  which  the  larger  number  of  atoms  is 
present,  some  would  be  left  over  after  the  action  is  com- 
plete. Suppose,  further,  that  the  weights  of  the  atoms  of 
two  elements  are  to  each  other  as  1  : 10.  Then,  if,  when 
these  two  elements  are  brought  together,  they  combine  in 
the  proportion  of  one  atom  of  one  to  one  atom  of  the 
other,  the  resulting  compound  would  contain  the  elements 
in  the  proportion  of  one  part  by  weight  of  one  to  ten  parts 
by  weight  of  the  other.  Or  if,  on  analyzing  a  compound 
of  two  elements,  we  find  that  it  contains  one  part  by 
weight  of  one  to  ten  parts  by  weight  of  the  other,  we 
might  conclude  that  the  weights  of  the  atoms  of  the  two 
elements  bear  to  each  other  the  ratio  1:10. 

If  matter  consists  of  atoms,  and  chemical  action  takes 
place  between  these  atoms,  we  can  understand  why  chemical 
action  takes  place  between  definite  weights  of  substances; 


ATOMIC   WEIGHTS.  213 

in  other  words,  we  see  a  probable  reason  for  the  law  of 
definite  proportions.  As  the  atoms  are  supposed  to  be  in- 
divisible, if  two  elements  combine  in  more  than  one  pro- 
portion with  each  other,  they  must  do  so  in  the  proportion 
of  one  atom  of  one  to  two  atoms  of  the  other,  or  one  to 
three,  or  two  to  three,  or  in  some  other  way  which  does  not 
involve  the  breaking-up  of  the  atoms.  If,  for  example,  two 
elements,  the  weights  of  whose  atoms  are  as  1  to  10,  com- 
bine in  the  proportion  of  one  atom  of  one  to  one  atom  of 
the  other,  the  resulting  compound  will  contain  the  ele- 
ments in  the  proportion  of  one  part  by  weight  of  one  to 
ten  parts  by  weight  of  the  other  element.  If  the  same  ele- 
ments combine  m  the  proportion  of  one  atom  of  the  first  to 
two  atoms  of  the  other,  then  the  resulting  compound  will 
contain  the  elements  in  the  proportion  of  one  part  by 
weight  of  one  to  twenty  parts  by  weight  of  the  other,  and 
so  on.  It  will  thus  be  seen  that  if  two  elements  combine  in 
more  than  one  proportion  with  each  other,  and  the  view 
that  matter  consists  of  atoms  of  definite  weight,  and  that 
chemical  action  takes  place  between  these  atoms  is  cor- 
rect, then  if  follows  that  the  elements  must  combine  in 
accordance  with  the  law  of  multiple  proportions. 

Atomic  Weights. — A  thorough  study  of  the  facts  has 
shown  that  the  atomic  theory,  as  suggested  by  Dalton,  is  the 
simplest  conception  which  can  be  formed  in  regard  to  the 
constitution  of  matter  which  will  satisfactorily  account  for 
the  laws  of  definite  and  multiple  proportions.  The  weights 
of  the  elements  which  have  thus  far  been  referred  to  as 
combining  weights  are,  in  accordance  with  the  theory,  the 
relative  weights  of  the  atoms,  or  the  atomic  weights.  The 
symbols  of  the  elements  represent  atoms  of  the  elements. 
Thus  H  represents  an  atom  of  hydrogen,  0  an  atom  of 


214  INTRODUCTION  TO  CHEMISTRY. 

oxygen,  Cl  an  atom  of  chlorine,  etc.  The  combining  weights, 
found  by  analyzing  compounds  in  which  these  elements 
occur,  are  H  =  1,  0  =  16,  and  01  =  35.5.  That  is  to  say, 
by  means  of  these  figures  we  can  always  represent  the  rel- 
ative quantities  of  the  elements  found  in  their  compounds. 
Hydrochloric  acid,  for  example,  contains  hydrogen  and 
chlorine  in  the  proportion  of  1  part  hydrogen  to  35.5  parts 
chlorine.  Hence  it  is  believed  that  the  weight  of  the 
atom  of  hydrogen  is  to  that  of  chlorine  as  I  to  35.5.  As 
hydrogen  enters  into  combination  in  smaller  proportion 
than  any  other  element,  its  combining  weight  or  atomic 
weight  is  taken  as  the  unit,  and  all  others  compared  with 
it.  If  we  say  that  the  atomic  weight  of  oxygen  is  16,  and 
that  of  chlorine  is  35.5,  we  mean  simply  that  the  atom  of 
oxygen  is  16  times  heavier  and  that  of  chlorine  35.5  times 
heavier  than  that  of  hydrogen.  We  might  take  any  other 
standard,  but  that  of  the  hydrogen  atom  is  the  simplest. 
At  one  time  the  atomic  weight  of  oxygen  was  taken  as  100, 
and  then  the  atomic  weights  of  the  other  elements  were 
relatively  larger. 

[PROBLEM. — If  we  called  the  atomic  weight  of  oxygen   100, 

what  would  those  of  hydrogen   and  chlorine   be?  The   atomic 

weight  of  hydrogen  being  accepted  as  1,  those  of  oxygen  and 
chlorine  are  16  and  35.5  respectively.] 

As  the  symbols  of  the  elements  represent  atoms,  so  the 
symbols  of  compounds  represent  combinations  of  atoms. 
The  formula  of  hydrochloric  acid,  HC1,  represents,  accord- 
ing to  the  theory,  the  smallest  particle  of  this  substance  that 
can  exist.  It  is  made  up  of  an  atom  of  hydrogen  and  an  atom 
of  chlorine,  which  are  chemically  combined.  The  formulas 
HN03,  H2S04,  HC10S,  etc.,  represent  the  smallest  par- 
ticles of  the  substances  that  can  exist.  The  smallest  particle 
of  nitric  acid  consists  of  1  atom  of  hydrogen,  1  atom  of 


ATOMIC  WEIGHTS. 

nitrogen,  and  3  atoms  of  oxygen;  the  smallest  particle  of 
sulphuric  acid  that  can  exist  consists  of  2  atoms  of  hydro- 
gen, 1  atom  of  sulphur,  and  4  atoms  of  oxygen;  the  small- 
est particle  of  chloric  acid  consists  of  1  atom  of  hydrogen,  1 
atom  of  chlorine,  and  3  atoms  of  oxygen.  These  smallest 
particles  of  compounds  are  called  molecules.  The  formula 
HN03  represents,  then,  a  molecule  of  nitric  acid,  H,0  a 
molecule  of  water,  HC1  a  molecule  of  hydrochloric  acid. 
The  molecules  are  made  up  of  atoms.  The  weight  of  a 
molecule  is  equal  to  the  sum  of  the  weights  of  the  atoms 
of  which  it  is  composed.  The  molecule  of  sulphuric  acid 
is  represented  by  H,S04.  The 

2  atoms  of  hydrogen  weigh 2  parts. 

1  atom  of  sulphur  weighs 32     " 

4  atoms  of  oxygen  weigh 64     " 

98     " 

The  sum  is  98.  Therefore,  the  weight  of  the  molecule 
of  sulphuric  acid  is  98  times  greater  than  the  weight  of 
the  atom  of  hydrogen. 

How  the  Relative  Weights  of  the  Atoms  are  Determined. 
— If  we  could  isolate  atoms  and  weigh  them,  there  would  be 
no  serious  difficulty  in  determining  their  relative  weights. 
But  as  we  cannot  deal  with  atoms,  we  must  deal  with 
masses  of  atoms,  and  from  a  study  of  these  masses  draw 
conclusions  regarding  the  weights  of  the  atoms. 

If  it  were  the  rule  that  two  elements  combine  with  each 
other  in  only  one  proportion,  it  might  be  safe  to  conclude 
that  they  combine  in  the  proportion  of  one  atom  of  one  to 
one  atom  of  the  other.  Then,  by  simply  determining  the 
relative  weights  of  the  elements  contained  in  a  mass  of  the 
compound,  we  would  be  in  a  position  to  draw  a  conclusion 


216  INTRODUCTION  TO  CHEMISTRY. 

regarding  the  relative  weights  of  the  atoms.  But  suppose 
two  elements  combine  in  more  than  one  proportion. 
Suppose,  for  example,  that  nitrogen  and  oxygen  combine, 
as  they  do,  in  these  proportions:  14  of  nitrogen  to  8  of 
oxygen,  7  of  nitrogen  to  8  of  oxygen,  7  of  nitrogen  to  1C 
of  oxygen,  and  it  is  required  from  these  figures  to  de- 
termine the  relative  weights  of  the  atoms  of  nitrogen  and 
oxygen.  We  may  suppose  that  in  the  first  compound  the 
elements  are  combined  atom  to  atom,  then  the  relative 
weights  of  these  atoms  are  14  for  nitrogen  to  8  for  oxygen. 
If,  however,  we  had  already  concluded  from  a  study  of  the 
compounds  of  hydrogen  and  oxygen  that  the  atom  of 
oxygen  is  16  times  heavier  than  that  of  hydrogen,  we 
should  have  in  the  above  compound  of  nitrogen  and  oxygen 
28  parts  of  nitrogen  combined  with  16  parts  of  oxygen, 
and  the  atomic  weight  of  nitrogen  would  appear  to  be  28. 
But  we  may  equally  well  assume  that  in  this  compound  2 
atoms  of  nitrogen  are  combined  with  1  atom  of  oxygen. 
This  idea  would  be  represented  by  the  formula  NaO,  and, 
if  we  accept  this  conception,  the  atomic  weight  of  nitrogen 
must  be  14.  This  example  will  suffice  to  show  that  the  de- 
termination of  the  relative  weights  of  atoms  by  means  of 
the  analyses  of  compounds  is  a  difficult  matter,  and  that 
attempts  to  make  the  determinations  in  this  way  would 
necessarily  lead  us  into  difficulties  which  we  could  not 
surmount  without  the  aid  of  some  new  conception  which 
will  aid  us  in  judging  of  the  number  of  atoms  contained 
in  the  molecules  of  compounds. 

Avogadro's  Hypothesis. — Early  in  this  century  the  Italian 
chemist  Avogadro  occupied  himself  with  the  study  of  the 
specific  gravities  of  gaseous  substances,  and  saw  clearly  that 
there  is  some  connection  between  the  figures  representing 


AVOGADRWS   HYPOTHESIS.  217 

the  relative  weights  of  equal  volumes  of  gases  and  those 
representing  the  combining  weights.  It  has  already  been 
pointed  out  that  the  weights  of  equal  volumes  of  hydrogen, 
chlorine,  and  oxygen  bear  to  one  another  the  same  relation 
as  their  combining  weights  (atomic  weights),  viz.,  1  :  35.5  : 
16.  The  same  relation  is  noticed  in  the  case  of  other  gases. 
This  fact,  taken  together  with  others  relating  to  the 
physical  properties  of  gases,  led  Avogadro  to  the  conception 
that  equal  volumes  of  all  gases  under  the  same  conditions  of 
temperature  and  pressure  contain  the  same  number  of  mole- 
cules. This  is  known  as  Avogadro's  hypothesis.  It  has 
been  tested  in  a  great  many  ways,  but  has  always  asserted 
itself  as  correct.  The  investigations  of  both  chemists  and 
physicists  have  only  tended  to  confirm  the  correctness  of 
the  conception,  and  at  the  present  day  it  forms  one  of  the 
most  important  foundations  of  thought  in  regard  to 
chemical  phenomena.  Let  us  see  how  it  helps  us,  and 
what  conclusions  it  leads  us  to. 

We  can  determine  the  weights  of  equal  volumes  of  gases 
without  difficulty.  According  to  the  hypothesis  of  Avo- 
gadro, these  weights  bear  to  one  another  the  same  relation 
that  the  weights  of  the  molecules  of  these  substances  do. 
Take,  for  example,  some  of  the  compounds  thus  far  con- 
sidered, which  are  gases  at  ordinary  temperatures,  or  can 
be  converted  into  gases  by  heat.  These  are  water,  hydro 
chloric  acid,  ammonia,  nitrous  oxide,  nitric  oxide,  marsh 
gas,  carbon  dioxide,  carbon  monoxide,  cyanogen,  hydro- 
cyanic acid.  The  specific  gravities  of  these  substances  in 
the  form  of  gas  or  vapor  have  been  determined.  They  are 
water,  0.623;  hydrochloric  acid,  1.247;  ammonia,  0.597; 
nitrous  oxide,  1.520;  nitric  oxide,  1.039;  marsh  gas,  0.557 
carbon  dioxide,  1.529;  carbon  monoxide,  0.9G8;  cyanogen, 


218 


INTRODUCTION  TO  CHEMISTRY. 


1.8;  hydrocyanic  acid,  0.948.  These  figures,  then,  express 
the  relative  weights  of  equal  volumes  of  the  gases,  and  they 
also  express  the  relation  between  the  weights  of  the  mole- 
cules of  the  substances.  It  is  only  necessary  to  adopt  some 
standard  to  which  we  can  refer  the  weights  of  other  mole- 
cules. We  may  conveniently  take  hydrochloric  acid.  The 
smallest  molecular  weight  which  we  can  adopt  for  this  com- 
pound without  making  the  atomic  weight  of  hydrogen  less 
than  unity  is  36.5,  for  hydrochloric  acid  consists  of  1  part 
by  weight  of  hydrogen  combined  with  35.5  parts  by  weight 
of  chlorine.  Hence,  if  the  sum  of  the  weights  of  its  atoms 
or  its  molecular  weight  were  less  then  36.5,  the  weight  of 
the  atom  of  hydrogen  would  be  less  than  1.  If  the  molec- 
ular weight  of  hydrochloric  acid  is  36.5,  it  is  an  easy  mat- 
ter to  calculate  the  molecular  weights  of  the  other  sub- 
stances mentioned,  for,  according  to  Avogadro's  hypothesis, 
they  bear  to  the  molecular  weight  of  hydrochloric  acid  the 
same  relation  that  their  specific  gravities  bear  to  the  spe- 
cific gravity  of  hydrochloric  acid.  The  results  of  the  cal- 
culation are  given  in  the  subjoined  table: 


COMPOUND. 

Sp.  Gr.  of  Gas 
or  Vapor. 

Calculated 
Molec.Weight. 

Water    

0.623 

18.1 

1.247 

36.5 

0.597 

17.4 

Nitrous  oxide      

1  52 

44.5 

1.039 

30.4 

Marsh  gas  

0.557 

16.3 

Carbon  dioxide     

1  529 

44.8 

Carbon  monoxide  

0  968 

28.3 

Cyanogen  

1.8 

52.6 

Hydrocyanic  acid. 

0  948 

27.7 

The  figures  thus  deduced  are  relatively  correct,  provided 
always  the  hypothesis  upon  which  the  calculation  is  based 
is  correct.  Now,  by  analysis,  we  find  that  in  18  parts  of 


ATOMIC   WEIGHTS. 

water  there  are  2  parts  of  hydrogen  and  16  parts  of  oxygen; 
in  hydrochloric  acid  there  are  1  part  of  hydrogen  and  35.5 
parts  of  chlorine;  in  ammonia,  14  parts  of  nitrogen  and  3 
parts  of  hydrogen;  in  nitrons  oxide,  28  parts  of  nitrogen 
and  16  parts  of  oxygen;  in  nitric  oxide,  14  parts  of  nitro- 
gen and  16  parts  of  oxygen;  in  marsh  gas,  12  parts  of  car- 
bon to  4  parts  of  hydrogen;  in  carbon  dioxide,  12  parts  of 
carbon  and  32  parts  of  oxygen;  in  carbon  monoxide,  12 
parts  of  carbon  and  16  parts  of  oxygen;  in  cyanogen,  24 
parts  of  carbon  and  28  parts  of  nitrogen;  in  hydrocyanic 
acid,  1  part  of  hydrogen,  12  parts  of  carbon,  and  14  parts  of 
nitrogen.  Knowing  the  weights  of  the  molecules  into 
which  an  element  enters,  and  the  relative  quantity  of  the 
element  present  in  these  molecules,  we  select  the  smallest 
quantity  of  the  element  that  enters  into  the  composition 
of  molecules  as  the  atomic  weight.  Thus,  for  example,  if 
we  were  to  examine  all  known  oxygen  compounds  that  can 
be  studied  in  the  form  of  gas  or  vapor,  we  should  find  that 
the  smallest  quantity  of  oxygen  found  in  any  molecule  is 
represented  by  16,  using  the  standard  already  adopted. 
Thus,  in  water,  to  make  up  the  molecular  weight,  18, 
we  have  16  parts  of  oxygen  and  2  parts  of  hydrogen  ; 
in  nitrous  oxide,  28  parts  of  nitrogen  and  16  parts  of 
oxygen;  in  carbon  dioxide,  12  parts  of  carbon  and  32  parts 
of  oxygen;  in  carbon  monoxide,  12  parts  of  carbon  and  16 
parts  of  oxygen.  We  therefore  select  16  as  the  atomic 
weight  of  oxygen. 

The  ratio  of  the  specific  gravity  of  a  gas  to  its  molecular 
weight  is  approximately  1  :  28.88,  i.e., 

=  28.  88,       or      M  =  d  X  28.  88,  * 


*  The  mere  ability  to  state  this  rule  is  of  no  value  to  the  student. 
What  he  should  attempt  to  learn,  and  with  an  effort  he  can  do  so, 


220  INTRODUCTION  TO  CHEMISTRY. 

in  which  M  represents  the  molecular  weight  of  a  gaseous 
compound,  and  d  its  specific  gravity  as  compared  with  air 
as  the  standard.  This  gives  us  the  molecular  weight  very 
nearly.  The  exact  figure  to  be  adopted  is  then  determined 
by  analysis. 

Molecules  of  the  Elements. — The  acceptance  of  Avoga- 
dro's  hypothesis  lead's  to  a  curious  conclusion  regarding  the 
structure  of  elementary  gases.  If  we  determine  the  molec- 
ular weights  of  hydrogen,  oxygen,  chlorine,  and  nitrogen, 
we  find  that  they  are  2,  32,  71,  and  28  respectively.  In 
other  words,  they  are  twice  as  great  as  their  atomic  weights. 
According  to  this,  these  gases  consist  of  molecules  which 
are  twice  as  heavy  as  their  atoms,  or,  in  other  words,  the 
molecules  of  these  elementary  gases  consist  of  two  atoms 
each.  •  The  same  conclusion  is  reached  by  another  line  of 
reasoning.  When  one  volume  of  hydrogen  combines  with 
one  volume  of  chlorine,  two  volumes  of  hydrochloric  acid  are 
formed.  Now,  as  equal  volumes  of  all  gases  contain  the  same 
number  of  molecules,  if  we  assume  that  in  a  certain  volume 
of  hydrogen  there  are  100  molecules,  then  in  the  same 
volume  of  chlorine  and  of  hydrochloric  acid  there  are 
also  100  molecules.  But  from  1  volume  containing  100 
molecules  of  hydrogen  and  1  volume  containing  100  mole- 
cules of  chlorine  we  get  2  volumes  containing  200  molecules 
of  hydrochloric  acid.  In  each  molecule  of  hydrochloric- 
acid  gas  there  must  be  at  least  one  atom  of  hydrogen  and 
one  atom  of  chlorine,  and  in  the  200  molecules  of  hydro- 
chloric acid  there  must  be  200  atoms  of  hydrogen  and  200 

is  the  facts  and  the  lines  of  thought  which  lead  to  the  adoption  of 
the  rule.  He  should  have  a  perfectly  clear  conception  in  regard  to 
the  meaning  of  the  terms  molecular  weight  and  specific  gravity,  and 
the  facts  which  led  to  the  discovery  of  the  relation  existing  between 
them. 


MOLECULES  OF  ELEMENTS. 

atoms  of  chlorine.  These  200  atoms  of  hydrogen,  however, 
must  have  been  contained  in  the  100  molecules  of  hydro- 
gen with  which  we  started,  and  similarly  the  200  atoms  of 
chlorine  must  have  been  contained  in  the  100  molecules  of 
chlorine.  Therefore,  each  molecule  of  hydrogen  must  con- 
sist of  at  least  2  atoms  of  hydrogen,  and  each  molecule  of 
chlorine  must  consist  of  at  least.  2  atoms  of  chlorine. 

A  similar  study  of  other  elementary  gases  leads  to  simi- 
lar conclusions  in  regard  to  their  molecules.  The  molecule 
of  a  few  elementary  gases  has  been  shown  to  consist  of  4 
atoms,  some  of  3  atoms,*  and  of  a  few  others  of  a  single 
atom;  but  usually  the  condition  appears  to  be  that  found 
in  hydrogen  and  chlorine.  The  view  is  thus  forced  upon 
us  that  the  molecules  of  elementary  gases  consist  of  atoms 
of  the  same  kind,  just  as  the  molecules  of  compound  gases 
consist  of  atoms  of  different  kinds.  The  molecule  of 
hydrogen  is  a  compound  of  two  atoms  of  hydrogen, 
just  as  the  molecule  of  hydrochloric  acid  is  a  compound 
of  an  atom  of  hydrogen  and  an  atom  of  chlorine.  Accord- 
ing to  this  conception,  when  hydrogen  gas  and  chlorine 
gas  are  brought  together,  the  complete  action  is  not  repre- 
sented by  the  equation 

H  +  01  =  HC1. 


*  In  speaking  of  ozone,  it  was  stated  that  when  oxygen  is  changed 
to  ozone  there  is  a  diminution  of  volume  from  three  to  two  without 
change  of  weight.  In  other  words,  the  specific  gravity  of  oxygen  is 
two  thirds  that  of  ozone.  But  the  specific  gravity  of  oxygen  leads  to 
the  conclusion  that  its  molecule  contains  two  atoms.  Similarly,  the 
specific  gravity  of  ozone  leads  to  the  conclusion  that  its  molecule  con- 
tains three  atoms.  We  therefore  conceive  ozone  to  be  made  up  of 
molecules  each  of  which  consists  of  three  atoms  of  oxygen;  and 
ordinary  oxygen  to  be  made  up  of  molecules  each  of  which  consists 
of  two  atoms  of  oxygen.  The  molecular  weight  of  ordinary  oxygen 
is  32,  and  that  of  ozone  is  48. 


222  INTRODUCTION  TO  CHEMISTRY. 

Before  we  can  get  atoms  of  hydrogen  or  chlorine,  the 
molecules  of  hydrogen  and  chlorine  must  first  be  broken 
up.  Hence,  there  are  two  acts  involved  in  passing  from 
hydrogen  gas  and  chlorine  gas  to  hydrochloric  acid.  These 
are: 

HH    +     C1C1     =     H  +  H  +  01  +  OL 

Molecule  of       Molecule  of  Atoms  of          Atoms  of 

hydrogen.          chlorine.  hydrogen.         chlorine. 

Then,  further,  the  atoms  combine  to  form  compound  mole- 
cules : 

H  +  H  +  01  +  Cl  =  2HC1. 

Or  we  may  write  the  equation  thus : 

H2      +      01,      =      2HOL 

Molecule  of         Molecule  of 
hydrogen.  chlorine. 

Again,  when  an  elementary  gas  such  as  hydrogen  or  oxy- 
gen is  set  free  from  a  compound,  we  are  led  to  believe  from 
considerations  like  the  above  that  at  the  instant  it  is  liber- 
ated it  exists  in  the  atomic  condition,  but  that  if  there  is 
nothing  else  present  with  which  the  atoms  combine,  they 
combine  with  each  other  to  form  molecules.  After  it  has 
been  set  free,  therefore,  it  should  be  less  active  than  at  the 
instant  it  is  set  free.  This  is  quite  in  accordance  with 
some  curious  and  well-known  facts. 

Nascent  State. — It  is  found  that  at  the  instant  elements 
are  set  free  from  their  compounds  they  are  capable  of 
effecting  changes  which  they  cannot  effect  after  they  have 
once  been  set  free.  Thus,  free  oxygen  gas  passed  into  hy- 
drochloric acid  produces  no  change  under  ordinary  condi- 
tions ;  but  oxygen  liberated  from  a  compound  in  contact 
with  hydrochloric  acid  decomposes  the  latter  and  sets 


NASCENT  STATE.  223 

chlorine  free.  Hydrogen  gas  passed  into  nitric  acid  causes 
no  change  ;  but  hydrogen  liberated  in  direct  contact  with 
nitric  acid  reduces  the  acid  and  forms  the  lower  oxides  of 
nitrogen.  Many  other  examples  of  this  kind  of  action 
might  be  cited.  The  simplest  explanation  of  the  phe- 
nomenon is  that  offered  above.  An  element  at  the  instant 
of  its  liberation  is  said  to  be  in  the  nascent  state. 

According  to  what  has  been  said,  all  substances,  element- 
ary as  well  as  combined,  appear  to  be  made  up  of  molecules. 
The  molecules  are  believed  to  have  the  properties  of  the 
substance  as  we  know  it  in  the  free  state.  The  molecule  is 
the  smallest  particle  of  a  substance  that  can  exist  in  the 
free  state.  The  molecules  are  said  to  be  held  together  by 
cohesion,  and,  theoretically,  a  substance  could  be  separated 
into  its  molecules  by  purely  mechanical  processes.  As  long 
as  action  upon  a  substance  does  not  pass  beyond  the  mole- 
cules, does  not  involve  decomposition  of  the  molecules,  the 
action  is  in  the  realm  of  physics.  The  molecules  are  made 
up  of  atoms,  which  are  held  together  by  chemical  affinity. 
The  atom  enters  into  chemical  action  and  is  the  smallest 
particle  of  a  substance  that  can  do  so.  Chemistry  is  the 
science  which  has  to  deal  with  changes  within  the  mole- 
cules. It  must  be  remembered  that  these  statements  are 
not  statements  of  facts  known  to  us.  The  laws  of  definite 
and  multiple  proportions  are  statements  of  facts;  but  when 
we  come  to  speak  of  atoms  and  molecules  we  are  dealing 
with  conceptions  which,  however  probable  they  may  appear, 
can  nevertheless  not  be  proved  to  be  true.  We  make  use 
of  these  conceptions  because  they  simplify  our  dealings  with 
the  facts  of  chemistry,  and  suggest  lines  of  inquiry  which 
lead  to  discoveries  of  value. 

How    a    Formula   is  Determined.— Chemical    formulas 


224  INTRODUCTION  TO  CHEMISTRY. 

were  first  introduced  for  the  purpose  of  expressing  the  com- 
position of  substances.  They  might  be  used  for  this  pur- 
pose at  present  without  having  any  connection  whatever 
with  the  conception  of  atoms  and  molecules,  but  the  dif- 
ficulty would  then  be  to  decide  upon  the  combining  weights 
of  the  elements.  It  would  be  possible  for  authoritative 
bodies  to  unite  in  issuing  an  edict  that  the  combining 
weights  of  the  elements  shall  be  certain  figures  which  are 
in  harmony  with  facts  known.  But  this  would  hardly  be 
a  scientific  mode  of  procedure  ;  and  there  might  exist 
differences  of  opinion  in  regard  to  the  advisability  of  ac- 
cepting the  figures.  When,  however,  we  once  accept  the 
atomic  theory  and  the  hypothesis  of  Avogadro,  we  have  a 
definite  basis  to  work  on,  and  there  is  little  opportunity  for 
disagreement  in  regard  to  the  figures  to  be  adopted. 

The  necessary  steps  in  the  determination  of  the  formula 
of  a  compound  may  be  illustrated  by  the  case  of  water.  The 
compound  is  first  analyzed  and  found  to  contain  hydrogen 
and  oxygen  in  the  proportion  of  1  part  hydrogen  to  8  parts 
oxygen.  This  is  a  fact.  But  we  wish  to  express  by  our 
formula  not  only  the  composition  of  the  substance,  but  the 
composition  of  a  molecule  of  the  substance.  We  therefore 
determine  the  molecular  weight  by  the  method  described 
above  by  comparing  the  specific  gravity  of  its  vapor  with 
that  of  hydrochloric  acid  or  hydrogen.  We  find  that  the 
molecular  weight  is  18.  In  other  words,  the  molecule  of 
water,  or  the  smallest  particle  of  water,  is  18  times  heavier 
than  an  atom  of  hydrogen.  According  to  the  analysis,  the 
18  parts  are  made  up  of  2  parts  of  hydrogen  and  16  parts 
of  oxygen.  By  an  examination  of  a  large  number  of 
gaseous  compounds  containing  oxygen  we  conclude  that 
16  is  the .  atomic  weight  of  oxygen,  as  this  is  the  smallest 


VALENCE.  225 

quantity  found  in  any  of  the  compounds.  Therefore,  the 
molecule  of  water  consists  of  2  atoms  of  hydrogen  weighing 
2  parts  and  1  atom  of  oxygen  weighing  16  parts.  The 
formula  representing  the  facts  and  conceptions  in  regard 
to  the  composition  of  water  is  H,0. 

Every  formula  is  intended  to  express  the  composition  and 
relative  weight  of  a  molecule  of  the  compound  represented. 
But  only  in  the  case  of  compounds  which  are  gases  or 
which  can  be  converted  into  vapors  have  we  a  definite  basis 
for  assuming  that  the  formulas  do  represent  the  relative 
weights  of  the  molecules. 

Valence. — The  formulas  of  the  compounds  thus  far  con- 
sidered have  all  been  determined  by  exactly  the  same 
methods.  On  comparing  the  formulas  of  the  hydrogen 
compounds  of  chlorine,  oxygen,  nitrogen,  and  carbon,  we 
cannot  fail  to  be  struck  by  certain  curious  differences  be- 
tween them.  The  formulas  are 

C1H    OH,    NH3     CH4. 

Speaking  in  terms  of  the  theory,  the  molecule  of  hydro- 
chloric acid  consists  of  1  atom  of  chlorine  combined  with  1 
atom  of  hydrogen;  the  molecule  of  water  consists  of  1 
atom  of  oxygen  combined  with  2  atoms  of  hydrogen;  the 
molecule  of  ammonia  consists  of  1  atom  of  nitrogen  com- 
bined with  3  atoms  of  hydrogen;  the  molecule  of  marsh 
gas  consists  of  1  atom  of  carbon  combined  with  4  atoms 
of  hydrogen.  "We  see,  thus,  that  the  atoms  of  chlorine, 
oxygen,  nitrogen,  and  carbon  differ  from  one  another  in 
their  power  of  holding  hydrogen  in  combination.  The 
oxygen  atom  has  twice  the  power  of  the  chlorine  atom, 
the  nitrogen  atom  has  three  times  this  power,  and  the  car- 
bon atom  has  four  times  this  power.  On  examining  the 
15 


226  INTRODUCTION  TO  CHEMISTRY. 

compounds  of  other  elements,  we  find  that  other  atoms 
differ  from  one  another  in  the  same  way. 

The  smallest  power,  as  far  as  the  number  of  other  atoms 
which  it  can  hold  in  combination  is  concerned,  is  that  of 
the  chlorine  atom.  And  as  one  chlorine  atom  can  hold 
but  one  atom  of  hydrogen  in  combination,  so  one  atom  of 
hydrogen  can  hold  but  one  atom  of  chlorine  in  combina- 
tion. Either  the  hydrogen  atom  or  the  chlorine  atom  may 
be  taken  as  an  example  of  the  simplest  kind  of  atom.  Any 
element  like  hydrogen  and  chlorine  is  called  a  univalent 
element;  an  element  like  oxygen  whose  atom  can  hold  two 
unit  atoms  in  combination  is  called  a  bivalent  element;  an 
element  like  nitrogen  whose  atom  can  hold  three  unit 
atoms  in  combination  is  called  a  trivalent  element;  an  ele- 
ment like  carbon  whose  atom  can  hold  four  unit  atoms  in 
combination  is  called  a  quadrivalent  element.  Most  ele- 
ments belong  to  one  or  the  other  of  these  four  classes, 
though  there  are  some  which  can  hold  five,  six,  and  even 
seven  unit  atoms  in  combination.  These  are,  however, 
rare,  and  for  our  present  purpose  they  will  require  but 
slight  notice. 

Valence  is  that  property  of  an  element  by  virtue  of  which 
its  atom  can  hold  a  definite  number  of  other  atoms  in  com- 
bination. 

[Calcium  forms  with  chlorine  the  compound  CaCl,. 
What  is  the  valence  of  calcium  ?  Potassium  and  sodium  form 
chlorides  of  the  formulas  KOI  and  NaCl  respectively.  What 
is  the  valence  of  these  elements  ?  Sulphur  forms  with 
hydrogen  a  compound  of  the  formula  SHa.  What  is  the 
valence  of  sulphur  ?] 

Keplacing  Power  of  Elements. — In  the  formation  of  salts, 
we  have  seen  that  the  hydrogen  of  acids  is  replaced  by 


VALENCE.  227 

metals.  In  such  cases  one  atom  of  a  univalent  metal  takes 
the  place  of  one  atom  of  hydrogen,  one  atom  of  a  bivalent 
metal  takes  the  place  of  two  atoms  of  hydrogen,  etc. 
Thus,  potassium  and  sodium  are  univalent.  An  atom  of 
either  takes  the  place  of  one  atom  of  hydrogen  in  forming 
salts.  In  the  formation  of  potassium  nitrate  from  nitric 
acid,  HNOS,  one  atom  of  potassium  replaces  the  one  atom  of 
hydrogen  in  the  molecule  of  nitric  acid  forming  the  salt 
KN03.  So,  also,  in  sodium  nitrate,  NaN03,  one  atom  of 
the  univalent  element  sodium  replaces  one  atom  of  hydro- 
gen. In  the  molecule  of  sulphuric  acid,  H3S04,  there  are 
two  atoms  of  hydrogen.  To  replace  these,  two  atoms  of  a 
univalent  element  are  required.  Thus,  potassium  sulphate 
is  K2S04,  and  sodium  sulphate  is  Na,S04.  Illustrations  of 
salts  containing  bivalent  metals  are  the  following:  Zinc 
sulphate,  ZnS04,  in  which  one  atom  of  the  bivalent  ele- 
ment zinc  replaces  the  two  atoms  of  hydrogen  in  sulphuric 
acid;  barium  sulphate,  BaS04,  in  which  one  atom  of  biva- 
lent barium  replaces  the  two  atoms  of  hydrogen  of  sul- 
phuric acid. 

When  a  bivalent  metal  forms  a  salt  with  an  acid  like 
nitric  acid,  which  contains  but  one  atom  of  hydrogen  in  the 
molecule,  it  is  believed  that  one  atom  of  the  metal  acts 
upon  two  molecules  of  the  acid,  thus: 


Cu      2HN0  =  Cu  N0          H. 


The  formula  of  zinc  nitrate  is  similar,  viz.  :  Zn(N03)2. 
In  the  case  of  trivalent  elements  the  matter  is  a  lit- 
tle more  complicated,  but  still  simple  enough  if  it  be 
borne  in  mind  that  a  univalent  atom  replaces  one  atom  of 


228  INTRODUCTION  TO  CHEMISTRY. 

hydrogen ;  a  bivalent  atom  replaces  two  atoms  of  hydro- 
gen ;  a  trivalent  atom  replaces  three  atoms  of  hydrogen, 
etc.,  etc.  We  have  already  had  some  examples  illustrating 
these  principles.  We  shall  meet  with  others  particularly 
in  connection  with  the  subject  of  salts. 

We  have  no  idea  what  the  cause  of  the  property  called 
valence  is.  The  property  is  undoubtedly  due  to  some  deep- 
seated  condition  of  the  atoms.  The  univalent,  bivalent, 
trivalent,  and  quadrivalent  elements  probably  differ  from 
one  another  in  some  fundamental  way.  This  is  indicated 
by  a  consideration  of  the  volumes  of  hydrogen,  chlorine, 
oxygen,  and  nitrogen  which  combine  with  one  another. 
As  we  have  seen,  1  volume  of  hydrogen  combines  with  1 
volume  of  chlorine,  forming  2  volumes  of  hydrochloric 
acid.  This  is  the  simplest  relation  conceivable.  Further, 
1  volume  of  oxygen  combines  with  2  volumes  of  hydro- 
gen, forming  2  volumes  of  water  vapor.  In  this  case 
we  get  2  volumes  of  the  product  from  3  volumes  of  the 
combining  gases.  Apparently  the  oxygen  so  influences 
the  hydrogen  as  to  cause  it  to  occupy  only  half  the  volume 
which  it  does  in  hydrochloric  acid.  In  the  combination 
of  nitrogen  and  hydrogen  to  form  ammonia  3  volumes  of 
hydrogen  combine  with  1  volume  of  nitrogen  to  form  2 
volumes  of  ammonia.  The  nitrogen  apparently  influences 
the  hydrogen,  so  that  in  the  compound  it  occupies  only 
one  third  the  volume  that  it  occupies  in  hydrochloric  acid. 
It  is  probable  that  similar  relations  exist  between  other 
tmivalent,  bivalent,  and  trivalent  elements. 

The  subject  of  valence  is  a  difficult  one  to  deal  with,  for 
the  reason  that  the  valence  of  an  element  is  not  fixed,  but 
varies  according  to  circumstances.  It  may  vary  (1)  ac- 
cording to  the  temperature.  In  general,  the  higher  the 


SUMMARY.  229 

temperature  the  less  the  valence.  Thus,  phosphorus, 
which  is  quinquivalent  towards  chlorine  at  ordinary  tem- 
peratures, as  is  shown  by  the  formation  of  the  compound 
PC16,  is  trivalent  towards  the  same  element  at  higher 
temperature,  as  is  shown  by  the  fact  that  when  heated  the 
compound  P01&  gives  off  chlorine  and  becomes  PC13. 

The  valence  of  the  element  may  vary  (2)  according  to 
the  chemical  character  of  the  element  with  which  it  com- 
bines. Thus,  phosphorus,  which  is  quinquivalent  towards 
chlorine  at  ordinary  temperatures,  is  trivalent  towards 
hydrogen,  as  is  shown  by  the  compound  PH3. 

Generally  speaking,  however,  each  element  shows  a  ten- 
dency to  act  with  a  particular  valence  ;  or  if  it  varies  at 
all,  the  variation  is  between  narrow  limits.  Nitrogen  ap- 
pears as  trivalent  and  quinquivalent ;  carbon  as  bivalent 
and  quadrivalent,  etc. 

Summary. — When  natural  laws  are  discovered  we  try  to 
find  out  the  causes.  In  suggesting  a  possible  cause  we 
form  an  hypothesis.  When  the  hypothesis  has  been  well 
tested  and  applies  to  a  large  number  of  related  facts,  it  is 
called  a  theory.  The  atomic  theory  was  proposed  to  ac- 
count for  the  laws  of  definite  and  multiple  proportions. 
According  to  the  atomic  theory  as  accepted  by  chemists, 
all  substances  consist  of  atoms  or  indivisible  particles  with 
definite  weights.  When  chemical  action  takes  place  it 
does  so  between  these  particles,  and  it  consists  either  in  a 
separation  or  a  union  of  these  particles.  The  relative 
weights  of  atoms  are  called  the  atomic  weights.  The  small- 
est particles  of  compounds  are  called  molecules.  It  is  im- 
possible by  means  of  analysis  alone  to  reach  definite  con- 
clusions in  regard  to  the  relative  weights  of  atoms. 

Avogadro's  hypothesis  that  equal  volumes  of  all  gases 


230  INTRODUCTION  TO  CHEMISTRY. 

under  the  same  conditions  of  temperature  and  pressure 
contain  the  same  number  of  molecules  was  suggested  by  a 
study  of  the  physical  properties  of  gases  and  a  comparison 
of  the  weights  of  equal  volumes  of  gases,  or  their  specific 
gravities,  with  the  combining  weights  as  found  by  analysis. 
The  molecular  weights  of  substances  bear  to  one  another 
the  same  relations  that  the  specific  gravities  of  their  gases 
or  vapors  do.  Owing  to  a  peculiarity  of  gases  and  vapors 
which  we  cannot  discuss  here,  their  specific  gravities  are 
not  exactly  proportional  to  their  molecular  weights.  They 
are  very  nearly  so.  From  the  specific  gravity  we  calculate 
the  molecular  weight,  and  then  by  analyzing  the  com- 
pounds we  determine  exactly  what  the  molecular  weight  is. 

After  analyzing  the  compounds  of  an  element  and  de- 
termining their  molecular  weights,  we  select  the  smallest 
quantity  of  the  element  that  occurs  in  any  of  the  com- 
pounds as  the  atom,  and  the  weight  of  this  quantity  as 
compared  with  the  weight  of  the  smallest  quantity  of 
hydrogen  found  in  any  of  its  compounds  taken  as  unity  is 
the  atomic  weight  of  the  element. 

Elementary  gases  and  vapors  are  made  up  of  molecules, 
which  in  turn  consist  of  atoms  of  the  same  kind.  Ele- 
ments are  more  active  in  the  nascent  state  than  in  the  free 
state,  probably  because  the  instant  they  are  set  free  the 
atoms  are  uncombined,  while  after  they  have  been  set  free 
these  atoms  are  combined  in  the  form  of  molecules. 

Formulas  of  compounds  are  intended  to  represent  the 
composition  of  molecules  and  their  relative  weights.  They 
rest  upon  analyses  and  determinations  of  the  specific  granty 
of  the  substances  in  the  form  of  gas  or  vapor. 

The  valence  of  an  element  is  the  property  by  virtue  of 
which  its  atom  has  the  power  to  hold  in  combination  a  cer- 


SUMMARY. 


tain  number  of  other  atoms.  Elements  are  called  univa- 
lent,  bivalent,  trivalent,  quadrivalent,  etc.,  according  as 
they  exhibit  the  simplest  valence  like  that  of  hydrogen  and 
chlorine,  or  double,  treble,  or  quadruple  this  valence. 

The  replacing  power  of  the  elements  is  determined  by 
the  valence.  An  atom  of  a  univalent  element  can  replace 
one  atom  of  hydrogen;  an  atom  of  a  bivalent  element  can 
replace  two  atoms  of  hydrogen. 


CHAPTER   XII. 
CLASSIFICATION  OF  THE  ELEMENTS. 

AKY  attempt  to  classify  objects  without  a  thorough 
knowledge  of  their  properties  must  necessarily  be  imper- 
fect. We  may  classify  men  according  to  various  proper- 
ties,— for  example,  as  tall  and  short,  as  stupid  and  intelli- 
gent, as  strong  and  weak,  as  white  and  colored,  etc.;  but 
any  such  classification  is  obviously  imperfect,  for  the  reason 
that  it  takes  into  account  only  a  few  properties  of  men. 
So,  also,  in  attempting  to  classify  the  elements  it  is  difficult 
to  reach  a  satisfactory  result,  for  the  reason  that  if  we 
make  one  set  of  properties  the  basis  of  classification,  it  is 
questionable  whether  there  may  not  be  more  fundamental 
properties  which  should  furnish  the  basis.  As  our  knowl- 
edge in  regard  to  the  fundamental  properties  of  the  ele- 
ments increases,  the  problem  of  classification  will  become 
simpler. 

The  chemical  properties  which  force  themselves  upon 
our  attention  most  prominently  in  whatever  field. of  chem- 
istry we  may  be  working  are  those  which  are  known  as 
acid  properties  and  basic  properties.  As  has  already  been 
pointed  out,  these  two  kinds  of  properties  are  complement- 
ary. Acid  properties  are  the  opposite  of  basic  properties, 
and  they  have  the  remarkable  power  of  being  able  to  de- 
stroy each  other  when  the  substances  possessing  them  are 
brought  together.  Whatever  developments  there  may  be  in 


CLASSIFICATION  OF  ELEMENTS.  333 

the  study  6'f  chemistry  in  the  future,  it  is  certain  that  the 
distinction  between  these  two  kinds  of  properties  will 
always  be  recognized  as  important.  In  general,  both  acids 
and  bases  contain  oxygen  and  hydrogen.  There  are  some 
elements  whose  compounds  with  hydrogen  and  oxygen  have 
basic  properties,  and  others  whose  compounds  with  hydrogen 
and  oxygen  have  acid  properties.  This  important  fact  may 
be  used  as  a  basis  for  a  partial  classification  of  the  elements. 
According  to  this,  we  have  (1)  acid-forming  elements  and 
(2)  base-forming  elements.  As  examples  of  the  first  class, 
the  elements  chlorine,  nitrogen,  and  carbon,  already  con- 
sidered, may  be  mentioned.  Examples  of  the  second  class 
are  sodium,  calcium,  magnesium,  copper,  iron,  zinc,  etc. 
The  last-mentioned  elements  are  generally  called  metals, 
and  those  mentioned  as  examples  of  acid-forming  ele- 
ments are  generally  called  non-metals.  The  line  between 
acid-forming  and  base-forming  elements  cannot  be  drawn 
sharply,  for  there  are  some  elements  which  form  both 
acids  and  bases,  according  to  the  relative  quantity  of  oxy- 
gen with  which  they  combine.  Thus,  antimony  forms 
acids  with  well-marked  properties,  and  also  other  com- 
pounds which  neutralize  acids,  and  are  therefore  bases. 
The  same  is  true  of  chromium,  manganese,  and  some 
other  elements.  On  the  other  hand,  there  are  several  ele- 
ments which  form  only  acids,  and  several  which  form  only 
bases;  and,  further,  those  which  form  both  acids  and  bases 
generally  show  a  tendency  in  one  direction.  In  dealing 
with  the  elements,  then,  these  differences  in  properties 
will  be  taken  into  account. 

Another  important  fact  which  is  soon  recognized  in 
studying  the  elements  is  that  they  fall  into  families  accord- 
ing to  their  general  chemical  properties,  the  members  of 


234  INTRODUCTION  TO  CHEMISTRY. 

the  same  family  showing  striking  resemblances  among  one 
another.  Thus,  we  have  the  chlorine  family,  which  in- 
cludes, besides  chlorine  itself,  bromine,  iodine,  and 
fluorine.  We  shall  soon  see  that  these  three  elements  re- 
semble chlorine  very  closely  indeed,  so  that  what  we  have 
already  learned  in  regard  to  chlorine  will  be  of  great  assist- 
ance to  us  in  studying  the  other  members  of  the  family. 
Further,  we  have  the  sulphur  family,  consisting  of  the 
closely  related  elements  sulphur,  selenium,  and  tellurium  ; 
the  potassium  family,  consisting  of  lithium,  sodium, 
potassium,  rubidium,  and  caesium ;  the  calcium  family, 
consisting  of  calcium,  barium,  strontium;  and  others.  In 
all  these  cases  the  resemblance  between  the  members  of  the 
same  family  is  striking.  While  it  is  an  easy  matter  to  recog- 
nize the  existence  of  these  families,  the  recognition  of 
any  connection  between  the  different  families  is  more  diffi- 
cult; and,  hence,  attempts  to  bring  all  the  elements  into  one 
general  scheme  of  classification  have  been  unsatisfactory, 
It  would  be  premature  to  discuss  the  subject  at  this  stage, 
as  the  discussion  would  necessitate  reference  to  many  mat- 
ters which  are  not  familiar  to  the  student.  The  plan 
which  will  be  followed  is  briefly  this :  The  elements  thus 
far  considered,  with  the  exception  of  hydrogen,  serve  as 
types  of  certain  classes,  or  as  representatives  of  families. 
Hydrogen  has  no  analogue  among  the  other  elements.  It 
is  not  a  member  of  any  family.  Oxygen,  too,  has  certain 
peculiarities  which  distinguish  it  from  most  other  elements. 
It  nevertheless  shows  some  resemblance  to  sulphur  in  the 
character  of  its  compounds,  and  the  two  are  usually  re- 
garded as  belonging  to  the  same  family.  Chlorine,  as 
already  stated,  belongs  to  a  family  of  which  bromine, 
iodine,  and  fluorine  are  the  other  members.  Nitrogen  be- 


CLASSIFICATION  Off  ELEMENTS.  235 

longs  to  a  family  of  which  phosphorus,  arsenic,  and  an- 
timony are  the  other  best-known  members.  Carbon  also 
belongs  to  a  family,  silicon  being  the  other  well-known 
member.  We  therefore  have  the  following  families  first 
to  deal  with  : 


CHLORINE  FAMILY. 
Chlorine, 
Bromine, 
Iodine, 
Fluorine. 

SULPHUR  FAMILY. 
Sulphur, 
Selenium, 
Tellurium. 

NITROGEN  FAMILY. 
Nitrogen, 
Phosphorus, 
Arsenic, 
Antimony. 

CARBON  FAMILY 
Carbon, 
Silicon. 

The  principal  members  of  these  families  are  acid-forming 
elements,  generally  called  non-metals,  or  metalloids.  In 
the  nitrogen  family,  however,  one  of  the  members  is  both 
acid-forming  and  base-forming.  There  is  a  gradation  in 
the  properties  as  we  pass  from  nitrogen  to  antimony. 

As  the  object  of  this  book  is,  not  to  present  a  systematic 
treatise  on  the  facts  of  chemistry,  to  serve  as  a  book  of 
reference,  but  rather  to  present  concisely  such  facts  as  serve 
to  illustrate  the  general  character  of  chemical  action  and 
the  general  principles  of  the  science  of  chemistry,  it  will 
not  be  necessary  to  go  into  details  in  dealing  with  these 
families.  One  member  of  each  family  having  been  treated 
comparatively  fully,  the  other  members  may  be  treated 
briefly.  It  will  thus  be  possible  to  get  a  clearer  idea  of  the 
principles  of  the  science  than  by  attempting  to  study  a 
large  number  of  facts  the  connection  between  which  can  be 
but  dimly  discerned,  if  discerned  at  all. 

After  the  acid-forming  elements  have  been  considered, 
the  base-forming  elements  will  be  taken  up  in  a  similar 
way;  but,  as  will  be  seen,  the  chemistry  of  the  acid-forming 
elements  exhibits  more  variety,  and  is  hence  better  adapted 
to  the  illustration  of  the  general  principles  of  the  science 
than  that  of  the  base-forming  elements,  so  that  the  latter 
need  not  be  treated  as  fully. 


CHAPTER  XIII. 

THE  CHLORINE  FAMILY:  CHLORINE,  BROMINE,  IODINE, 
FLUORINE. 

THE  three  members  of  this  family  which  show  the  most 
marked  resemblance  are  chlorine,  bromine,  and  iodine. 
Fluorine  is  not  known  in  the  free  state,  but  only  in  com- 
pounds. These,  however,  resemble  the  compounds  of 
chlorine  in  some  respects,  and  hence  the  element  is  gen- 
erally included  in  this  family, 

Bromine,  Br  (At.  Wt.  80). — This  element  occurs  in 
nature  in  company  with  chlorine.  Chlorine,  as  has  been 
stated,  occurs  mostly  in  combination  with  sodium,  as 
sodium  chloride,  or  common  salt.  In  several  of  the  great 
salt-beds  there  is  some  bromine  in  the  form  of  sodium 
bromide,  NaBr,  and  in  some  places  it  occurs  as  potassium 
bromide,  KBr. 

The  process  of  preparation  of  bromine  is  exactly  the 
same  as  that  made  use  of  for  extracting  chlorine.  It  wili 
be  remembered  that  in  order  to  get  chlorine  out  of  sodium 
chloride  the  salt  is  first  converted  into  hydrochloric  acid, 
and  this  is  then  oxidized.  So,  too,  in  order  to  get  bromine 
out  of  sodium  bromide,  it  must  first  be  converted  into 
hydrobromic  acid,  and  this-then  oxidized.  The  reactions 
involved  are  usually: 

SNaBr  +  H3S04  =  Na,S04 
SHBr  +  0  =  H,0  +  2Br. 


BROMINE.  237 

As  in  the  case  of  chlorine,  the  substance  commonly  used 
is  manganese  dioxide,  when  the  reaction  takes  place  accord- 
ing to  the  following  equation : 

4HBr  +  MnOa  =  MnBr,  +  2HaO  +  2Br. 

[Refer  back  to  the  explanation  of  this  reaction  given 
under  the  head  of  chlorine.  What  other  methods  might 
be  used  in  the  preparation  of  bromine  ?] 

Bromine  is  a  heavy  dark  red  liquid  at  ordinary  tempera- 
tures. It  is  easily  converted  into  vapor  which  is  brownish 
red.  At  —24°  it  is  solid.  It  has  an  extremely  disagreeable 
smell,  to  which  fact  it  owes  its  name  (from  fipob^ios,  a 
stench). 

Its  properties  are,  in  general,  like  those  of  chlorine.  It 
acts  violently  upon  organic  substances.  It  attacks  the 
skin  and  the  membranes  lining  the  passages  of  the  throat 
and  lungs  in  much  the  same  way  as  chlorine.  Wounds 
caused  by  the  liquid  coming  in  contact  with  the  skin  are 
painful  and  serious.  It  must  be  handled  with  great  car 
With  water  at  low  temperatures  it  forms  a  hydrate  cor- 
responding to  chlorine  hydrate,  of  the  formula  Br2.10H20, 
which  decomposes  when  left  in  contact  with  the  air  at 
ordinary  temperatures.  It  dissolves  slightly  in  water,  form- 
ing a  colored  solution  called  bromine  water. 

Its  chemical  conduct  is  also  like  that  of  chlorine.  It 
combines  with  many  elements  directly  and  with  great  avid- 
ity. Its  combination  with  arsenic  and  some  other  ele- 
ments is  accompanied  by  an  evolution  of  light  and  heat,  as 
in  the  case  of  chlorine.  Its  compounds  with  other  ele- 
ments are  called  bromides.  While  acting  in  general  in  the 
same  way  as  chlorine,  it  is  a  somewhat  weaker  element,  so 
that  chlorine  drives  it  out  of  its  compounds  and  sets  it 
free. 


238  INTRODUCTION  TO  CHEMISTRY. 

EXPERIMENT  102.  —  Mix  together  3.5  grams  potassium 
bromide  and  7  grams  manganese  dioxide.  Put  the  mixture 
into  a  500  cc.  flask  ;  connect  with  a  condenser  (see  Fig. 
^8).  Mix  15  cc.  concentrated  sulphuric  acid  and  90  cc. 
water.  After  cooling  pour  the  liquid  on  the  mixture  in 
the  flask.  Gently  heat,  when  bromine  will  be  given  off  in 
the  form  of  vapor.  A  part  of  this  will  condense  and  col- 
lect in  the  receiver.  Perform  this  experiment  under  a 
hood  with  a  good  draught.  In  treating  the  manganese 
dioxide  and  potassium  bromide  together  with  sulphuric 
acid,  the  action  takes  place  as  represented  in  the  following 
equation  : 

2KBr  +  Mn02  +  2H2S04  =K2S04+MnS04  +  2 


Hence  there  are  left  behind  in  the  flask  both  potassium 
sulphate,  K2S04,  and  manganese  sulphate,  MnS04. 

[When  sulphuric  acid  acts  upon  manganese  dioxide  the 
action  takes  place  thus  : 

Mn02  +  H2S04  =  MnS04  +  H20  +  0. 

If  this  action  took  place  in  the  presence  of  hydrobromic 
acid,  what  effect  would  the  liberated  oxygen  have  ?  Suppose 
the  oxygen  were  allowed  to  escape  from  the  flask  containing 
th,e  manganese  dioxide  and  sulphuric  acid,  and  then  passed 
into  hydrobromic  acid,  would  the  same  result  be  reached  as 
when  the  hydrobromic  acid  is  in  the  flask  in  which  the 
oxygen  is  liberated  ?  "What  is  the  commonly  accepted  ex- 
planation ?  If  the  formula  of  manganese  sulphate  is 
MnS04,  what  is  the  valence  of  manganese  ?  What  would 
you  expect  the  formula  of  manganese  chloride  to  be  ?  Of 
manganese  oxide  ?  Is  the  valence  of  manganese  greater 
toward  oxygen  or  toward  chlorine?] 


ETDROBROMIG  ACID.  239 

Hydrobromic  Acid,  HBr. — Tlie  only  compound  which 
bromine  forms  with  hydrogen  alone  is  hydrobromic  acid. 
This  is  in  all  respects  very  much  like  hydrochloric  acid.  li 
is  made  in  the  same  way.  It  is  a  colorless  gas,  which 
forms  fumes  in  the  air  in  consequence  of  its  attraction  for 
moisture.  Its  solution  in  water  acts  very  much  like  ordinary 
hydrochloric  acid.  The  elements  are  not  held  together  as 
firmly  in  hydrobromic  as  in  hydrochloric  acid.  This  is 
shown  by  its  decomposition  under  circumstances  in  which 
hydrochloric  acid  is  stable.  Thus,  for  example,  it  is  de- 
composed by  sulphuric  acid,  while  hydrochloric  acid  is 
not.  The  hydrogen  is  separated  from  the  bromine  and  acts 
upon  the  sulphuric  acid,  while  the  bromine  is  given  off  as 
such.  Hence,  when  potassium  bromide  is  treated  with 
sulphuric  acid,  hydrobromic  acid  is  given  off,  together  with 
bromine  and  a  compound  of  sulphur  and  oxygen  which  is 
formed  by  the  action  of  hydrogen  on  the  sulphuric  acid. 

EXPEEIMENT  103. — In  a  small  porcelain  evaporating- dish 
put  a  few  crystals  of  potassium  bromide.  Pour  on  them  a 
few  drops  of  concentrated  sulphuric  acid.  The  white  fumes 
of  hydrobromic  acid  and  the  reddish-brown  vapor  of  bro- 
mine are  noticed.  Treat  a  few  crystals  of  .potassium  or 
sodium  chloride  in  the  same  way.  What  difference  is  there 
between  the  two  cases  ? 

Compounds  with  Hydrogen  and  Oxygen. — "With  hydrogen 
and  oxygen  bromine  forms  compounds  which  resemble  very 
closely  those  which  chlorine  forms  with  the  same  elements. 
The  principal  ones  are  Iromic  and  liypobromous  acids.  The 
potassium  salt  of  bromic  acid,  HBr03,  is  formed  by  treat- 
ing a  strong  solution  of  caustic  potash  with  bromine: 

6Br  +  6KOH  =  5KBr  -f-  KBrO,  +  3H80. 


240  INTRODUCTION  TO  CHEMISTRY. 

The  potassium  salt  of  hypobromous  acid,  HBrO,  is 
formed  by  treating  a  dilute  solution  of  caustic  potash  with 
bromine: 

2Br  +  2KOH  =  KBr  +  KBrO  +  H20. 

Iodine,  I  (At.  Wt.  127). — This  element  occurs  in  nature 
in  combination  with  sodium,  in  company  with  chlorine  and 
bromine,  but  in  smaller  quantity  than  either.  It  is  also 
found  in  larger  quantities  in  all  sea  plants.  It  is  obtained 
largely  from  the  latter  source.  On  the  coasts  of  Scotland 
and  France  the  sea-weed  which  is  thrown  up  by  storms  is 
gathered,  dried,  and  burned.  The  organic  portions  are  thus 
destroyed  [What  is  the  meaning  of  the  word  destroyed  used 
in  this  sense  ?]  and  the  mineral  or  earthy  portions  are  left 
behind  as  ashes.  This  incombustible  residue  is  called  kelp. 
It  contains  sodium  iodide.  Sea-weed  is  also  cultivated  for 
the  sake  of  the  sodium  iodide  contained  in  it.  Chili  salt- 
petre, or  the  natural  sodium  nitrate  found  in  Chili,  contains 
some  sodium  iodide,  and  of  late  this  has  furnished  a  con- 
siderable quantity  of  the  iodine  of  commerce. 

Iodine  is  obtained  from  sodium  iodide  just  as  chlorine 
and  bromine  are  obtained  from  their  compounds  with 
sodium  and  potassium.  [Give  the  equations  representing 
the  steps  which  must  be  taken  in  order  to  separate  iodine 
from  sodium  iodide.] 

At  ordinary  temperatures  iodine  is  a  grayish-black  crys- 
tallized solid.  It  is  volatile  at  ordinary  temperatures.  It 
melts  at  a  temperature  a  few  degrees  above  that  of  boiling 
water,  and  boils  at  a  somewhat  higher  temperature,  when  it 
is  converted  into  a  violet  vapor. 

EXPERIMENT  104. — Mix  together  about  2  grams  of  sodium 
or  potassium  iodide  and  4  grams  manganese  dioxide.  Treat 


IODINE  241 

with  a  little  sulphuric  acid  in  a  one  to  two  litre  flask.  Heat 
gently  on  a  sand-bath.  Gradually  the  vessel  will  be  filled 
with  the  beautiful  colored  vapor  of  iodine.  In  the  upper 
parts  of  the  flask  some  of  the  iodine  will  be  deposited  in 
the  form  of  crystals  of  a  grayish-black  color. 

The  action  of  iodine  is,  in  general,  the  same  as  that  of 
chlorine  and  bromine,  only  its  affinities  are  weaker.  Hydro- 
bromic  acid,  as  we  have  seen,  is  a  weaker  compound  than 
hydrochloric  acid.  Hydriodic  acid  is  still  weaker.  Chlorine 
acting  upon  hydromic  acid  sets  bromine  free.  Chlorine 
and  bromine  set  iodine  free  from  hydriodic  acid. 

Iodine  dissolves  slightly  in  water,  easily  in  alcohol,  and 
easily  in  a  water  solution  of  potassium  iodide. 

EXPERIMENT  105. — Make  solutions  of  iodine  in  water, 
in  alcohol,  and  in  a  water*  solution  of  potassium  iodide. 
Use  small  quantities  in  test-tubes. 

When  a  solution  containing  free  iodine  is  treated  with  a 
little  starch  paste,  the  solution  turns  blue,  in  consequence 
of  the  formation  of  a  complicated  compound  of  starch  and 
iodine.  Bromine  and  chlorine  do  not  form  blue  com- 
pounds. Advantage  is  taken  of  this  fact  to  distinguish 
between  iodine  and  other  members  of  the  same  family. 

EXPERIMENT  106. — Make  some  starch  paste  by  covering 
a  few  grains  of  starch  in  a  porcelain  evaporating-dish  with 
cold  water,  grinding  this  to  a  paste,  and  pouring  200-300 
cc.  boiling  hot  water  on  it.  After  cooling  add  a  little  of 
this  paste  to  a  dilute  water  solution  of  iodine.  The  solu- 
tion will  turn  blue  if  the  conditions  are  right.  Now  add 
a  little  of  the  paste  to  a  diluted  water  solution  of  potassium 
iodide.  There  is  no  change  of  color,  because  the  iodine  is 
in  combination  with  the  potassium.  Add  a  drop  or  two  of 
a  solution  of  chlorine  in  water,  when  the  blue  color  will 


242  INTRODUCTION  TO  CHEMISTRY. 

appear.  The  explanation  of  this  phenomenon  is  that  the 
chlorine  sets  the  iodine  free,  and  the  free  iodine  then  acts 
upon  the  starch,  producing  the  blue  compound.  [How  can 
you  show  that  the  chlorine  itself  will  not  form  a  blue  com- 
pound with  starch?] 

Hydriodic  acid,  HI,  is  analogous  to  hydrochloric  and 
hydrobromic  acids.  It  is  set  free  from  its  compounds  by 
treating  them  with  sulphuric  acid,  but  it  is  even  more  un- 
stable than  hydrobromic  acid,  and  hence  breaks  up  into 
hydrogen  and  iodine.  The  iodine  is  liberated,  while  the 
hydrogen  acts  on  the  sulphuric  acid,  as  it  does  in  the  case 
of  hydrobromic  acid. 

EXPEEIMENT  107. — Treat  a  few  crystals  of  potassium 
iodide  with  sulphuric  acid.  [What  do  you  notice?]  Com- 
pare the  result  with  that  obtained  in  the  case  of  potassium 
bromide  and  sodium  chloride. 

The  principal  compound  of  iodine  with  hydrogen  and 
oxygen  is  iodic  acid,  HI03,  which  is  the  analogue  of  chlo- 
ric and  bromic  acids.  It  is  known  principally  in  the  form 
of  its  potassium  salt,  potassium  iodate,  KI03.  When 
heated,  this  salt,  like  the  chlorate  and  the  brornate,  gives 
up  all  its  oxygen,  potassium  iodide,  KI,  being  left  be- 
hind. 

Fluorine  occurs  in  nature  in  large  quantity,  and  widely 
distributed,  but  always  in  combination  with  other  ele- 
ments. It  is  found  chiefly  in  combination  with  calcium, 
as  fluor-spar,  or  calcium  fluoride,  CaF2,  and  in  combination 
with  sodium  and  aluminium,  as  cryolite,  a  mineral  which 
occurs  abundantly  in  Greenland,  and  has  the  composition 
3NaF.  A1F3,  being  a  complex  compound  of  sodium  fluoride 
and  aluminium  fluoride. 

All  attempts  to  obtain  fluorine  in  the  free  state  have 


HTDROFL  UORIC  ACID.  243 

failed.  This  appears  to  be  due  to  the  extraordinary  power 
which  fluorine  has  of  combining  with  other  substances. 
This  power  causes  it  to  combine  with  the  materials  of  which 
the  vessels  in  which  it  is  liberated  are  made. 

Hydrofluoric  acid,  HF,  is  made  from  fluor-spar  by  treat- 
ing it  with  sulphuric  acid.  The  action  is  of  the  same 
character  as  that  which  takes  place  when  hydrochloric  acid 
is  liberated  from  sodium  chloride: 

CaF,  +  H3S04  =  CaS04  +  2HF. 

It  is  a  colorless  gas,  with  strong  acid  properties.  It 
greatly  irritates  the  membranes  lining  the  respiratory  or- 
gans, and  hence  care  should  be  taken  not  to  inhale  it.  It 
acts  upon  glass,  dissolving  it,  and  must  therefore  be  kept 
in  vessels  of  rubber,  lead,  or  platinum,  upon  which  it  does 
not  act.  Its  action  on  glass  consists  in  the  transformation 
of  silicon  dioxide,  or  silica,  Si02,  which  is  contained  in  all 
kinds  of  glass,  into  silicon  tetrafluoride,  SiF4,  which  is  a 
gas.  The  action  is  represented  thus: 

SiO,  +  4HF  =  SiF4  +  2HaO. 

EXPERIMENT  108. — In  a  lead  or  platinum  vessel  put  a 
few  grams  (5-6)  of  powdered  fluor-spar  and  pour  on  it 
enough  concentrated  sulphuric  acid  to  make  a  thick  paste. 
Cover  the  surface  of  a  piece  of  glass  with  a  thin  layer  of 
wax  or  paraffin,  and  through  this  scratch  some  letters  or 
figures,  so  as  to  leave  the  glass  exposed  where  the  scratches 
are  made.  Put  the  glass  over  the  vessel  containing  the 
fluor-spar,  and  let  it  stand  for  some  hours.  Take  off  the 
glass,  scrape  off  the  coating,  and  the  figures  which  were 
marked  through  the  wax  or  paraffin  will  be  found  etched 
on  the  glass. 


244  INTRODUCTION  TO  CHEMISTRY. 

The  acid  is  used  for  etching  glass,  particularly  for  mark- 
ing scales  on  thermometers,  barometers,  and  other  gradu- 
ated glass  instruments.  A  solution  of  the  gas  in  water  is 
manufactured  for  this  purpose  and  kept  in  rubber  bottles. 

Fluorine  does  not  combine  with  oxygen.  It  is  the  only 
element  of  which  this  statement  can  be  made. 

Comparison  of  the  Members  of  the  Chlorine  Family. — In 
considering,  first,  the  physical  properties  of  these  elements, 
we  notice  that  all,  with  the  exception  of  fluorine,  form 
colored  gases  or  vapors.  At  ordinary  temperatures  chlo- 
rine is  a  gas,  bromine  a  liquid,  and  iodine  a  solid.  In  re- 
gard to  their  chemical  conduct,  it  may  be  said  that,  in  gen- 
eral, fluorine  exhibits  the  strongest  affinity  for  elements 
with  which  it  combines  at  all;  chlorine  comes  next  in 
order,  then  bromine,  and  lastly  iodine.  This  is  seen  par- 
ticularly in  the  relative  stability  of  their  compounds  with 
hydrogen.  Their  compounds  with  metals  also  show  the 
same  relation.  On  the  other  hand,  with  oxygen  the  order 
is  reversed.  Fluorine  does  not  unite  with  oxygen  at  all. 
The  compounds  of  chlorine  and  oxygen  are  very  unstable; 
those  with  bromine  rather  more  stable;  and  one  compound 
of  iodine  and  oxygen  is  comparatively  stable. 

The  elements  of  this  family  combine  with  hydrogen  and 
with  other  elements  in  the  simplest  way.  They  are  all 
univalent. 

The  compounds  formed  by  the  three  elements  chlorine, 
bromine,  and  iodine  with  hydrogen  and  oxygen  have  analo- 
gous composition,  and  are  formed  by  analogous  reactions. 
Thus,  we  have  the  hydrogen  compounds: 

HOI,  HBr,  and  HI ; 


TUB  CHLORINE  FAMILY.  245 

and  the  compounds  with  hydrogen  and  oxygen: 

HC10          HBrO 
HC100 


HC10*        HBr03        HI08 
HC104        HBr04        HI04 

The  properties  of  any  compound  of  one  element  are  simi- 
lar to  those  of  the  compounds  of  analogous  composition  of 
the  other  elements  of  the  family. 

All  these  facts  seem  to  indicate  that  these  elements  are 
not  distinct  forms  of  matter  entirely  independent  of  one 
another,  but  rather  that  they  contain  some  common  con- 
stituent. This  idea  is  apparently  confirmed  by  a  consid- 
eration of  their  combining  or  atomic  weights,  which  are  ae 
follows: 

Chlorine,     35.5; 

Bromine,     80; 

Iodine,       127. 

On  comparing  these  it  will  be  seen  that  the  atomic 
weight  of  bromine,  80,  is  nearly  the  mean  of  the  atomic 
weights  of  chlorine  and  iodine,  or  at  least  near  enough  to 

arrest  attention.     We  have  35.5  +  127  =  162.5,  and  -^- 

A 

=  81.25.  The  properties  of  these  elements  vary  with  the 
variations  in  their  atomic  weights,  or  with  the  weights  of 
their  atoms.  The  gradation  in  properties  takes  place  in  the 
order  chlorine,  bromine,  iodine,  and  this  is  also  the  order 
in  which  the  atomic  weights  increase.  This  may  be  a  mere 
accident,  but  we  shall  find  that  in  the  other  families  we 
meet  with  similar  indications  of  a  close  connection  between 
the  weights  of  the  atoms  of  the  elements  and  their  physical 
and  chemical  properties.  And  so  closely  has  this  connec- 


246  INTRODUCTION  TO  CHEMISTRY. 

tion  been  traced  out  that  it  now  appears  possible  to  foretell 
the. properties  of  an  element  if  we  know  its  atomic  weight. 
Why  there  should  be  this  remarkable  connection  we  do  not 
know.  Doubtless,  continued  investigation  of  chemical 
phenomena  will  eventually  lead  to  the  discovery  of  some 
reason  for  it.  At  present  the  facts  have  not  been  studied 
sufficiently  deeply  to  enable  us  to  form  any  probable  con- 
ception in  regard  to  the  cause.  It  is  not  impossible  that 
what  we  call  elements  may  be  compounds  of  a  few  still 
simpler  substances;  but  however  attractive  such  speculation 
may  be,  it  is  not  profitable  unless  it  leads  to  further  work 
for  the  purpose  of  proving  its  soundness  or  of  refuting  it. 
The  discovery  of  a  direct  relation  in  composition  between 
the  members  of  the  same  family  of  elements  would  furnish 
a  basis  for  profitable  speculation.  Such  a  discovery  would 
rank  in  importance  with  the  discovery  that  heat  and 
motion  are  convertible  one  into  the  other. 


CHAPTER  XIV. 

THE  SULPHUR  FAMILY: 
SULPHUR,  SELENIUM,  TELLURIUM. 

Sulphur,  S.  (At.  Wt.  32).— The  principal  member  of 
this  family  is  sulphur.  In  nature  it  is  frequently  found 
accompanied  by  small  quantities  of  selenium,  and  some- 
times by  tellurium.  It  has  been  known  in  the  elementary 
form  from  the  earliest  times,  for  the  reason  that  it  occurs 
abundantly  in  this  form  in  nature.  It  is  found  particu- 
larly in  the  neighborhood  of  volcanoes,  as  in  Sicily,  which 
is  the  chief  source  of  the  sulphur  of  commerce.  It  occurs, 
further,  in  combination  with  many  metals  as  sulphides, — as 
in  iron  pyrites,  FeS2;  copper  pyrites,  FeCuS, ;  galenite, 
PbS,  etc. ;  in  combination  with  metals  and  oxygen  as  sul- 
phates,— for  example,  as  calcium  sulphate,  or  gypsum, 
CaS04 +  2H20;  barium  sulphate,  or  heavy  spar,  BaS04 ; 
lead  sulphate,  PbS04 ;  in  a  few  vegetable  and  animal 
products  in  combination  with 'carbon,  hydrogen  and,  gen- 
erally, with  nitrogen. 

Extraction  of  Sulphur  from  its  Ores. — When  taken  from 
the  mines,  sulphur  is  mixed  'with  many  earthy  substances 
from  which  it  must  be  separated.  This  separation  is  accom- 
plished by  piling  the  ore  in  such  a  way  as  to  leave  passages 
for  air.  The  piles  are  covered  with  material  to  prevent 
free  access  of  air,  and  the  mass  is  then  lighted  below.  A 
part  of  the  sulphur  burns,  and  the  heat  thus  furnished 
melts  the  rest  of  the  -sulphur.  The  molten  sulphur  runs 


248  INTRODUCTION  TO  CHEMISTRY. 

down  to  the  bottom  of  the  pile,  and  is  drawn  off  from  time 
to  time.  If  the  pile  were  not  protected  from  free  access  of 
air,  the  sulphur  would  burn  up,  yielding  a  gas,  sulphur 
dioxide,  S02. 

[What  analogy  is  there  between  this  process  and  that 
made  use  of  in  making  charcoal  ?  What  are  the  essential 
differences  between  the  two  processes  ?] 

The  crude  brimstone  thus  obtained  is  afterwards  refined 
by  distillation,  and  it  is  this  distilled  sulphur  which  we 
meet  with  in  the  market  under  the  names  "roll  brimstone" 
and  "  flowers  of  sulphur/'  The  distillation  is  carried  on 
in  earthenware  retorts  connected  with  large  chambers  of 
brick- work.  When  the  vapor  of  sulphur  first  comes  into 
the  condensing-chamber  it  is  suddenly  cooled,  and  hence 
deposited  in  the  form  of  a  fine  powder.  This  is  what  is 
called  "flowers  of  sulphur."  After  the  distillation  has 
continued  for  some  time,  the  vapor  condenses  in  the  form 
of  a  liquid,  which  collects  at  the  bottom  of  the  chamber. 
This  is  drawn  off  into  wooden  moulds  and  takes  the  form 
of  "roll  brimstone"  or  "  stick  sulphur/' 

Properties. — Sulphur  is  a  yellow,  brittle  substance  which 
at  —50°  is  almost  colorless.  It  melts  at  111°,  forming  a  thin, 
straw-colored  liquid.  When  heated  to  a  higher  tempera- 
ture it  becomes  darker  and  darker  in  color,  and  at  200°  to 
250°  it  is  so  viscid  that  the  vessel  in  which  it  is  contained 
may  be  turned  upside  down  without  danger  of  -its  running 
out.  Finally,  at  440°  it  boils  and  is  then  converted  into  a 
brownish-yellow  vapor. 

EXPEEIMENT  109.— Distil  about  10  grams  of  roll  sul- 
phur from  an  ordinary  glass  retort.  Notice  the  changes 
above  described.  Collect  the  liquid  sulphur  which  passes 
over  in  a  beaker  glass  containing  cold  water. 


CRYSTALLOGRAPHY.  249 

When  molten  sulphur  solidifies,  or  when  it  is  deposited 
from  a  solution,  its  particles  arrange  themselves  in- regular 
forms  called  crystals.  But,  strange  to  say,  the  crystals 
formed  from  molten  sulphur  are  entirely  different  from 
those  deposited  from  solutions  of  sulphur.  The  former  are 
honey-yellow  needles.  The  latter  are  octahedrons  with 
rhombic  base,  which  is  also  the  form  of  the  sulphur  found 
in  nature.  A  careful  examination  of  the  needles  shows  that 
the  angles  which  their  faces  form  with  one  another  are  not 
the  same  as  the  angles  formed  by  the  faces  of  the  octahe- 
drons, and  that  the  crystals  are  constructed  on  a  different 
plan.  The  needles  belong  to  the  monoclinic  system  of  crys- 
tals, and  the  octahedrons  to  the  rhombic  system. 

Crystallography. — Notwithstanding  the  infinite  number 
of  forms  assumed  by  solids  in  passing  from  the  liquid  to  the 
solid  state  and  when  deposited  from  solutions,  it  has  been 
shown  that  all  can  be  referred  to  a  very  few  systems. 
Usually  six  systems  are  adopted.  These  are  : 

1.  THE  REGULAR  SYSTEM.    All  the  crystals  belonging  to 
this  system  can  be  referred  to  three  axes  of  equal  length, 
and  at  right  angles  to  one  another,  crossing  at  the  centre. 
Examples  of  crystals  belonging  to  this  system  are  the  regu- 
lar octahedron  and  the  cube.     The   three   axes   are   the 
imaginary  lines  which  pass  through  the  solid  angles  of  the 
octahedron.     All  the  other  forms  of  this  system  may  be 
referred  to  this  octahedron. 

2.  THE  TETRAGONAL  SYSTEM.     In  this  tho  forms  are 
referred  to  three  axes  at  right  angles,  two  of  equal  length 
and  one  differing  from  the  other  two.     The  fundamental 
forms  are  the  octahedron  and  prism. 

3.  THE  HEXAGONAL  SYSTEM,    The  crystals  of  this  sys- 
tem are  referred  to  four  axes, — three  of  equal  length  in- 


250  INTRODUCTION  TO  CHEMISTRY. 

cliued  at  60°  to  one  another,  and  a  fourth  at  a  right 
angle  to.  them,  and  either  of  the  same  length  or  different 
length.  The  six-sided  pyramid  and  prism  are  the  principal 
forms. 

4.  THE  EHOMBIC   SYSTEM.     The  crystals  belonging  to 
this  system  have  three  axes  of   unequal  lengths  at  right 
angles  to  one  another. 

5.  THE  .  MOKOCLINIC  SYSTEM.     In  this  system  the  crys- 
tals have  three  axes, — two  at  right  angles  to  each  other, 
the  third  at  right  angles  to  one  and  inclined  to  the  other. 

6.  THE  TRICLIHTC  SYSTEM.     The  crystals  belonging  to 
this  system  are  referred  to  three  axes,  all  inclined  to  one 
another. 

The  subject  of  crystallography  is  one  that  cannot  be 
made  clear  in  a  few  words.  It  requires  careful  study  and 
much  practice  in  observing  forms  of  crystals.  From  what 
has  just  been  said,  however,  it  will  be  seen  that  the  system 
of  classification  of  crystals  is  a  simple  one.  For  our  pres- 
ent purpose,  the  fact  should  be  specially  emphasized  that 
the  crystalline  form  of  a  substance  is  a  very  definite  prop- 
erty, by  means  of  which  it  may  be  distinguished  from  other 
substances.  The  fact  that  a  substance  crystallizes  in  the 
regular  system  is  just  as  characteristic  of  that  substance  as 
the  fact  that  it  boils  or  melts  at  a  certain  point.  Thus,  we 
know  that  ice  always  melts  at  0°,  and  that  water  solidifies 
at  0°.  We  should  be  much  surprised  to  find  water  solidi- 
fying at  some  other  temperature,  say  20°.  Similarly, 
knowing  that  sulphur  occurs  in  nature  crystallized  in 
forms  which  belong  to  the  rhombic  system,  we  are  natu- 
rally surprised  to  find  that,  when  molten  sulphur  solidifies, 
it  crystallizes  in  forms  belonging  to  the  monoclinic  system. 
What  is  perhaps  still  stranger  is  the  fact  that  when  the 


SULPHUR. 

honey-yellow  needles  are  allowed  to  stand  unmolested  they 
spontaneously  undergo  a  change.  They  become  opaque; 
their  color  changes;  and  now,  if  examined  carefully,  they 
are  found  to  consist  of  minute  crystals  like  those  found  in 
nature.  It  is  evident  that  the  arrangement  of  the  particles 
in  the  monoclinic  crystals  of  sulphur  is  not  a  stable  one. 

Substances  which  crystallize  in  two  distinct  forms  are 
called  dimorphous.  Carbon  crystallizes  in  two  different 
forms  [what  are  they?],  and  is  hence  dimorphous. 

EXPERIMENT  110. — In  a  covered  sand  or  Hessian  cruci- 
ble melt  about  25  grams  of  roll  sulphur.  Let  it  cool  slow- 
ly, and  when  a  thin  crust  has  formed  on  the  surface  make 
a  hole  through  this  and  pour  out  the  liquid  part  of  the 
sulphur.  The  inside  of  the  crucible  will  be  found  lined 
with  the  honey-yellow  needles  which,  as  has  been  stated, 
belong  to  the  monoclinic  system.  Take  out  a  few  of  the 
crystals  and  examine  them.  [Are  they  brittle  or  elastic? 
What  is  their  color?  Are  they  opaque,  transparent,  or 
translucent?]  Lay  the  crucible  aside,  and  in  the  course  of 
a  few  days  again  examine  the  crystals.  [What  changes,  if 
any,  have  taken  place?] 

Sulphur  can  also  be  obtained  in  the  amorphous,  or  un- 
crystallized,  condition.  That  which  was  collected  under 
water  in  Experiment  109  will  be  found  to  be  soft  and  dough- 
like.  It  is  amorphous.  After  a  time  it  becomes  brittle. 

When  separated  from  a  compound  which  is  dissolved  in 
water,  it  is  finely  divided,  and  gives  the  liquid  an  appear- 
ance suggesting  milk. 

Sulphur  is  insoluble  in  water,  slightly  soluble  in  alcohol 
and  ether.  It  dissolves  in  the  liquid  compound  of  carbon 
and  sulphur  known  as  carbon  bisulphide,  OS2,  and  from 
this  solution  it  is  deposited  in  rhombic  crystals. 


252  INTRODUCTION  TO  CHEMISTRY. 

EXPERIMENT  111. — Dissolve  2  to  3  grams  roll  sulphur  in 
5  to  10  cc.  carbon  bisulphide.  Put  the  solution  in  a  shal- 
low vessel,  and  allow  the  carbon  bisulphide  to  evaporate  by 
standing  in  the  air.  The  sulphur  will  remain  behind  in 
the  form  of  crystals. 

Sulphur  combines  with  oxygen  when  heated  to  a  suffi- 
ciently high  temperature.  The  product  is  sulphur  dioxide, 
S02.  [Is  there  any  analogy  between  carbon  and  sulphur 
in  this  respect?]  It  combines  readily  with  most  metals, 
forming  sulphides,  which  are  in  some  respects  analogous  to 
the  oxides.  Its  combination  with  iron  has  already  been 
shown  in  Experiment  10.  It  also  combines  with  copper, 
the  act  being  accompanied  by  light  and  heat. 

EXPERIMENT  112.— In  a  wide  test-tube  heat  some  sul- 
phur to  boiling.  Introduce  into  it  small  pieces  of  copper 
foil  or  sheet  copper.  Or  hold  a  narrow  piece  of  sheet  cop- 
per so  that  the  end  just  dips  into  the  boiling  sulphur. 

Hydrogen  Sulphide,  Sulphuretted  Hydrogen,  H2S. — When 
hydrogen  is  passed  over  highly  heated  sulphur,  the  two 
elements  combine  to  form  hydrogen  sulphide.  [Is  there 
any  analogy  between  this  process  and  the  formation  of 
water  by  the  burning  of  hydrogen?]  This  compound  of 
sulphur  and  hydrogen  occurs  in  nature  in  solution  in  the 
so-called  sulphur  waters,  which  are  met  with  in  many  parts 
of  this  country  as  well  as  in  other  countries.  It  also  issues 
from  the  earth  in  some  places.  It  is  formed  by  heating 
organic  substances  which  contain  sulphur,  just  as  water  is 
formed  by  heating  organic  substances  which  contain  oxy- 
gen, and  ammonia  by  heating  such  as  contain  nitrogen. 
It  is  formed,  further,  by  decomposition  of  organic  sub- 
stances which  contain  sulphur,  as,  for  example,  the  albu- 


HYDROGEN  SULPHIDE.  2.~<3 

men  of  eggs.     The  odor  of  rotten  eggs  is  partly  due  to  the 
formation  of  hydrogen  sulphide. 

In  the  laboratory  the  gas  is  made  most  readily  by  treat- 
ing a  sulphide  with  an  acid.  When  a  metal,  as  iron,  is 
treated  with  sulphuric  acid,  hydrogen  is  given  off  and  the 
iron  salt  of  the  acid  is  formed  thus  : 

Fe  +  H2S04  =  FeS04  +  H2. 

When  sulphuric  acid  acts  upon  the  oxide  of  iron,  hydro- 
gen is  given  off  in  combination  with  oxygen  as  water, 
thus : 

FeO  +  H2S04  =  FeS04  +  H20. 

Finally,  when  sulphuric  acid  acts  upon  iron  sulphide, 
hydrogen  is  given  off  in  combination  with  sulphur  as  hy- 
drogen sulphide,  thus  : 

FeS  +  H2S04  =  FeS04  +  H,S. 

A  similar  explanation  holds  for  other  acids  as  well  as 
sulphuric  acid.  For  example,  when  hydrochloric  acid  acts 
upon  iron  sulphide,  the  action  takes  place  as  represented  in 
the  equation 

2HC1  +  FeS  =  FeC]2  +  H2S. 

EXPERIMENT  113. — Ariange  an  apparatus  as  shown  in 
Fig.  47.  Put  a  small  handful  of  the  sulphide  of  iron, 
FeS,  in  the  flask,  and  pour  dilute  sulphuric  acid  upon  it. 
Pass  the  evolved  gas  through  a  little  water  contained  in 
the  wash  cylinder  A.  Pass  some  of  the  gas  into  water. 
[What  evidence  have  you  that  it  dissolves?]  Collect  some 
by  displacement  of  air.  Its  specific  gravity  is  1.178. 
[Should  the  vessel  be  placed  with  the  mouth  down  or  up?] 


254 


INTRODUCTION  TO  CHEMISTRY. 


Set  fire  to  some  of  the  gas  contained  in  a  cylinder.  If 
there  is  free  access  of  air,  the  sulphur  burns  to  sulphur  di- 
oxide and  the  hydrogen  to  water. 

[What  are  the  products  of  combustion  of  marsh  gas?] 
When  treated  with  chlorine,  bromine,  or  iodine,  sulphur 


is  deposited  and  the  hydrogen  combines  with  the  other 
element.  Thus,  with  chlorine  the  action  takes  place  as 
represented  in  the  equation 

HaS  +  C12  =  2HC1  +  S. 

[Does  chlorine  ever  act  in  a  similar  way  on  water?  Un- 
der what  circumstances?  What  is  the  peculiarity  of  the 
oxygen  given  off?] 

Most  metals  when  heated  in  the  gas  are  converted  into 
sulphides.  Thus,  when  it  is  passed  over  heated  iron  this 
reaction  takes  place: 

Fe  +  H3S  =  FeS  +  Hr 


CHEMICAL  ANALYSIS.  255 

[What  takes  place  when  water  vapor  is  passed  over 
heated  iron?] 

Many  of  the  sulphides  are  insoluble  in  water.  Hence, 
when  hydrogen  sulphide  is  passed  through  solutions  con- 
taining metals  in  the  forms  of  soluble  salts,  the  insoluble 
sulphides  are  thrown  down,  or  precipitated. 

EXPEEIMENT  114. — Pass  hydrogen  sulphide  successively 
through  solutions  containing  a  little  lead  nitrate,  zinc 
sulphate,  and  arsenic  prepared  by  dissolving  a  little 
white  arsenic,  or  arsenic  trioxide,  Asa03,  in  dilute  hydro- 
chloric acid.  In  the  vessel  containing  the  lead  a  black 
precipitate  of  lead  sulphide  will  be  formed;  in  the  one  con- 
taining the  zinc  sulphate  there  will  be  formed  a  white  pre- 
cipitate of  zinc  sulphide;  in  the  one  containing  the  arsenic, 
a  straw-yellow  precipitate  of  arsenic  sulphide  will  be 
formed.  In  all  these  cases  the  hydrogen  of  the  sulphur- 
etted hydrogen  and  the  metal  of  the  salt  exchange  places. 
For  example,  in  the  case  of  zinc  sulphate  the  reaction 
takes  place  thus : 

ZnS04  +  H2S  =  ZnS  +  H2S04. 

Chemical  Analysis. — In  dealing  with  chemical  substances 
the  first  thing  we  have  to  determine  is  their  composition, 
or,  in  other  words,  we  have  to  analyze  them.  For  this 
purpose  we  must  first  know  the  properties  of  the  elements 
and  their  general  conduct  towards  chemical  substances.  To 
facilitate  the  process  of  analysis  the  mixture  to  be  exam- 
ined is  usually  brought  into  solution  and  then  treated  suc- 
cessively with  certain  substances,  the  effect  being  observed 
in  each  case.  Suppose  we  had  a  solution  containing  most 
of  the  metallic  elements  in  the  form  of  salts.  If  we  were  to 
pass  through  this  solution  hydrogen  sulphide,  some  of  the 


256  INTRODUCTION  TO   CHEMISTRY. 

metals  would  be  precipitated  in  the  form  of  sulphides, 
while  others  would  remain  in  solution,  as  their  sulphides 
are  soluble.  We  then  filter  off  the  precipitate  and  exam- 
ine it  by  other  methods,  and  we  could  also  further  examine 
the  solution  from  which  the  sulphides  were  precipitated. 
By  adding  to  this  another  reagent  which  will  precipitate 
some  of  the  metals  and  leave  the  others  in  solution,  we 
learn  still  more  in  regard  to  the  composition  of  the  sub- 
stance under  examination.  Hydrogen  sulphide  is  con- 
stantly made  use  of  in  the  laboratory  for  the  purposes  of 
analysis. 

Hydrosulphides. — When  hydrogen  sulphide  acts  upon 
hydroxides,  the  action  consists  in  the  formation  of  hydro- 
sulphides.  In  the  case  of  potassium  hydroxide  the  action 
takes  place  thus: 

KOH  +  H2S  =  KSH  +  H20. 

The  oxygen  and  sulphur  simply  exchange  places. 

If  only  half  enough  hydrogen  sulphide  is  passed  into  the 
solution  to  effect  the  above  change,  a  sulphide  is  formed 
thus: 

2KOH  +  H2S  =  K2S  +  2H20. 


sulphide  be  allowed  to  act  on  potassium 
sulphide,  the  product  is  potassium  hydrosulphide: 

K2S  +  H2S  =  2KSH. 

COMPOUNDS    OF    SULPHUR  WITH    OXYGEN"   AND   WITH   HY- 
DROGEN  AND   OXYGEN. 

When  sulphur  burns  in  the  air  it  forms  the  dioxide  S02. 
Under  certain  conditions  the  dioxide  combines  with  more 


SULPHUR  DIOXIDE.  257 

oxygen,  forming  the  trioxide  SO,.     When  sulphur  dioxide 
acts  upon  water,  sulphurous  acid  is  formed: 

SO,  +  H20  =  HaS08. 

• 

[What  analogy  is  there  between  the  acid  thus  formed 
and  carbonic  acid  ?] 

When  the  trioxide  combines  with  water,  sulphuric  acid  is 
formed: 

S03  +  H20  -  H2S04. 

Sulphur  Dioxide,  S02. — This  compound  is  formed  by 
burning  sulphur  in  the  air  or  in  oxygen.  It  issues  from 
volcanoes  in  large  quantities.  It  is  best  prepared  by  treat- 
ing copper  with  sulphuric  acid.  The  action  does  not  take 
place  without  the  aid  of  heat.  We  would  naturally  expect 
the  copper  simply  to  take  the  place  of  the  hydrogen  of  the 
acid: 

Cu-+  H2S04  =  CuS04  +  2H. 

This  is  probably  the  first  action  that  takes  place.  But 
the  hydrogen  acts  upon  the  sulphuric  acid,  reducing  it  and 
forming  sulphur  dioxide: 

HaS04  +  2H  =  2HaO  +  S0a. 

[Compare  the  action  of  copper  on  sulphuric  acid  with 
that  of  copper  on  nitric  acid.  What  analogy  is  there  be- 
tween the  two  cases?  What  difference?] 

EXPEEIMENT  115. — Put  eight  or  ten  pieces  of  sheet  cop- 
per, one  to  two  inches  long  and  about  half  an  inch  wide,  in  a 
500  cc.  flask;  pour  15  to  20  cc.  concentrated  sulphuric  acid 
on  it.  On  heating,  sulphur  dioxide  will  be  evolved.  The 
17 


258  INTRODUCTION  TO  CHEMISTRY. 

moment  the  gas  begins  to  come  off,  lower  the  flame,  and 
keep  it  at  such  a  height  that  the  evolution  is  regular  and 
not  too  active.  Pass  some  of  the  gas  into  a  bottle  contain- 
ing water.  Collect  a  vessel  full  by  displacement  of  air.  Its 
specific  gravity  is  2.24.  See  whether  the  gas  will  burn  or 
support  combustion. 

Sulphur  dioxide  is  a  colorless  gas  of  an  unpleasant,  suffo- 
cating odor,  familiar  to  every  one  as  that  of  burning  sul- 
phur-matches. Water  absorbs  it  readily. 

Sulphurous  Acid,  H2S03. — The  solution  in  water  has  acid 
properties,  and  probably  contains  the  acid  H2S03.  By 
neutralizing  the  solution  with  bases,  the  sulphites,  or  salts 
of  sulphurous  acid,  are  obtained.  The  sulphites  are  anal- 
ogous to  the  carbonates  in  composition,  and  suffer  the  same 
decomposition  when. treated  with  acids.  When  a  carbonate 
is  treated  with  an  acid,  carbon  dioxide  is  given  off.  So, 
also,  when  a  sulphite  is  treated  with  an  acid,  sulphur  diox- 
ide is  given  off: 

NajSO. .+  HaS04  =  Na,S04  +  H20  +  S0a, 
Na3S03  +  2HC1  =  2NaCl  +  H30  +  S03. 

When  a  solution  of  sulphur  dioxide  is  allowed  to  stand  in 
the  air  in  loosely  stoppered  bottles,  it  takes  up  oxygen,  the 
sulphurous  acid  being  converted  into  sulphuric  acid: 

H,S08  +  0  =  HaS04. 

Sulphur  dioxide  is  a  good  bleaching  agent,  and  is  exten- 
sively used  for  the  purpose  of  bleaching  wool,  silk,  straw, 
paper,  etc.  In  some  cases  the  bleaching  is  due  to  the  fact 
that  the  sulphur  dioxide  extracts  oxygen  from  the  colored 


SULPHURIC  ACID.  259 

substances,  forming  colorless  products.  In  other  cases 
the  action  is  more  complicated. 

EXPERIMENT  116. — Burn  a  little  sulphur  in  a  porcelain 
crucible  under  a  bell  jar.  Place  over  the  crucible  on  a 
tripod  some  flowers.  In  the  atmosphere  of  sulphur  diox- 
ide the  flowers  will  be  bleached. 

Sulphur  dioxide  has  the  power  to  check  fermentation, 
and  is  used  to  preserve  liquids  which-  have  a  tendency  to 
undergo  fermentation. 

Its  principal  use  is  in  the  manufacture  of  sulphuric  acid. 
For  this  purpose  it  is  made  in  enormous  quantities. 

Sulphuric  Acid,  H2S04. — Sulphuric  acid  is  found  in  nature 
in  the  form  of  salts,  as  gypsum,  heavy  spar,  etc.  It  cannot 
easily  be  prepared  from  its  salts,  as  nitric  acid  and  hydro- 
chloric acids  are,  and  is  made  exclusively  by  oxidizing  sul- 
phur dioxide  in  the  presence  of  water,  or,  in  other  words, 
by  oxidizing  sulphurous  acid.  The  reactions  involved  in 
the  manufacture  of  sulphuric  acid  are: 

S  +  02  =  S02, 

S02  +  H20  =  H2S03, 

H2S03  +  0  =  H2S04. 

The  last  reaction  cannot  readily  be  effected  directly  by 
the  action  of  the  oxygen  of  the  air,  but  an  extremely  inter- 
esting method  has  been  devised  by  which  the  oxygen  can 
be  constantly  transferred  from  the  air  to  the  sulphurous 
acid.  This  method  depends  partly  upon  the  power  of  ni- 
tric oxide,  NO,  to  combine  directly  with  air  to  form  nitro- 
gen peroxide,  N02.  Nitrogen  peroxide  oxidizes  sulphur- 
ous acid,  and  is  itself  reduced  to  nitric  oxide.  If,  therefore, 
sulphur  dioxide,  water,  and  nitric  oxide  be  brought  to- 
gether, the  first  action  is  represented  thus: 


260  INTRODUCTION  TO  CHEMISTRY. 

S02  +  H20  +  N0a  =  H2S04  +  NO. 

Now,  if  air  be  supplied,  the  nitric  oxide  will  be  converted 
into  the  peroxide: 

NO  +  0  =  N02. 

The  peroxide  acting  upon  a  further  quantity  of  sulphur 
dioxide  and  water  is  again  reduced,  and  so  on  indefinitely. 
It  will  thus  be  seen  that,  starting  with  a  small  quantity  of 
nitric  oxide,  it  should  be  possible  to  convert  a  large  quantity 
of  sulphur  dioxide  into  sulphuric  acid. 

In  the  manufacture  of  sulphuric  acid,  sulphur  is  burned 
and  the  sulphur  dioxide  conducted  into  large  chambers 
lined  with  lead.  The  reason  why  lead  is  used  is  that  sul- 
phuric acid  acts  upon  most  other  available  substances.  In- 
stead of  starting  with  nitric  oxide,  nitric  acid  is  passed 
into  the  chambers,  and  water  in  the  form  of  steam.  The 
first  action  between  the  nitric  acid,  steam,  and  sulphur 
dioxide  is  this: 

2HN03  +  3S02  +  2HaO  =  3H2S04  +  2NO. 

From  this  point  we  have  to  deal  with  sulphur  dioxide, 
water,  and  nitric  oxide,  and  the  chief  reactions  are  those 
which  are  described  above. 

The  acid  obtained  from  the  chambers  contains  about  64 
per  cent  of  sulphuric  acid.  It  is  evaporated  in  lead  pans 
until  it  reaches  the  specific  gravity  1.75.  As  stronger  acid 
acts  upon  lead,  the  evaporation  is  carried  on  beyond  this  in 
platinum  or  glass.  The  strong  acid  thus  obtained  is  the 
concentrated  sulphuric  acid  of  commerce.  It  is  com- 
monly called  oil  of  vitriol. 

It  is  an  oily  liquid,  usually  somewhat  colored  by  impuri- 


SULPHURIC  ACID.  261 

ties.  The  pure  acid  is  a  colorless  liquid  at  ordinary  tem- 
peratures. When  cooled  down  it  forms  crystals.  It  is  a 
very  strong  acid,  decomposing  the  salts  of  most  other  acids, 
setting  the  acids  free,  and  appropriating  the  metals.  We 
have  already  had  illustrations  of  this  power  in  the  libera- 
tion of  nitric  and  hydrochloric  acids  from  their  salts  by 
treatment  with  sulphuric  acid. 

[Give  the  equations  representing  the  action  which  takes 
place  when  common  salt  and  potassium  nitrate  are  treated 
with  sulphuric  acid.] 

Sulphuric  acid  has  a  very  strong  tendency  to  absorb 
water,  and  to  form  compounds  with  it.  The  simplest  of 
these  is  the  hydrate  H2S04  +  H20.  This  is  a  crystallized 
substance  which  melts  at  a  low  temperature  (7.5°).  In 
consequence  of  the  formation  of  these  hydrates,  a  great 
deal  of  heat  is  evolved  when  sulphuric  acid  is  mixed  with 
water.  This  fact  has  been  repeatedly  illustrated  in  experi- 
ments already  performed;  and  the  necessity  for  precaution 
in  mixing  the  two  liquids  has  been  emphasized.  The  acid 
acts  upon  organic  substances  containing  hydrogen  and 
oxygen,  and  extracts  these  elements  in  the  proportions  to 
form  water.  If  a  piece  of  wood  be  put  in  the  acid  it  is 
charred,  in  consequence  of  the  abstraction  of  hydrogen  and 
oxygen.  [How  is  wood  usually  charred  in  the  preparation 
of  charcoal  ?  Is  there  any  analogy  between  the  preparation 
of  charcoal  in  the  ordinary  way  and  by  the  action  of  sul- 
phuric acid  ?]  Wounds  caused  by  sulphuric  acid  are  pain- 
ful and  difficult  to  heal. 

The  acid  is  used  for  the  purpose  of  drying  gases  upon 
which  it  does  not  act.  [Can  it  be  used  for  drying  ammo- 
nia ?"] 

Monobasic  and  Dibasic  Acids. — Sulphuric  acid  differs 


262  INTRODUCTION  TO  CHEMISTRY. 

markedly  from  nitric  and  hydrochloric  acids  in  one  respect. 
Jt  has  the  power  to  form  two  different  salts  with  the  same 
metal,  in  one  of  which  there  is  twice  as  much  metal  as  in 
the  other.  If  to  a  given  quantity  of  sulphuric  acid  there 
be  added  only  half  the  quantity  of  caustic  potash  required 
to  neutralize  it,  a  salt  is  formed  which  crystallizes.  It  has 
the  composition  represented  by  the  formula  KHS04.  If 
nitric  acid  be  treated  in  the  same  way,  only  half  the  acid  is 
acted  on,  and  this  forms  ordinary  potassium  nitrate,  KNO,, 
the  rest  of  the  acid  being  left  unacted  upon.  In  the  case 
of  sulphuric  acid  two  reactions  are  possible,  viz.  : 

H2S04  +  KOH  =  KHS04  +H  20,  and 
H2S04  +  2KOH  =  K2S04  +  2H.O. 

In  the  case  of  nitric  acid,  only  one  reaction  seems  to  be 
possible  : 

HN03  +  KOH  =  KN03  +  H20. 


Acids  which,  like  sulphuric  acid,  have  the  power  to 
form  two  salts  with  the  same  metal  are  called  dibasic  acids. 
Acids  which,  like  nitric  acid,  have  the  power  to  form  only  one 
salt  with  the  same  metal  are  called  monobasic  acids.  This 
power  is  connected  with  the  number  of  replaceable  hydro- 
gen atoms  contained  in  the  molecule  of  the  acids.  An  acid 
containing  two  replaceable  hydrogen  atoms  in  its  molecule 
is  dibasic;  one  containing  one  replaceable  hydrogen  atom 
in  its  molecule  is  monobasic. 

Acid,  Neutral,  and  Normal  Salts.  —  A  dibasic  acid  yields 
two  classes  of  salts:  (1)  those  in  which  all  the  hydrogen  is 
replaced,  and  (2)  those  in  which  half  the  hydrogen  is  re- 
placed by  metal.  The  former  are  called  normal  salts,  the 


SELENIUM  AND  TELLURIUM.  263 

latter  acid  salts.     Normal  salts  are  generally  neutral,  and 
are  sometimes  called  neutral  salts. 

Other  Acids  Containing  Sulphur. — Besides  sulphurous 
and  sulphuric  acids,  sulphur  forms  several  other  acids. 
These  cannot  be  considered  here.  Their  names  and  for- 
mulas are  as  follows : 

Hydrosulphurous  acid,  H2S02;  Pyrosulphuric  acid,  H2S207; 
Thiosulphuric  acid,  H2S203;      Trithionic  acid,  H2S306; 
Dithionic  acid,  H2S206;  Tetrathionic  acid,  H2S406. 


The  sodium  salt  of  thiosulphuric  acid,  NaaS308,  com- 
monly called  sodium  hyposulphite,  is  used  in  photography. 
Pyrosulphuric  acid)  or  fuming  sulphuric  acid,  breaks  up 
into  sulphuric  acid  and  sulphur  trioxide,  H2S207  =  H2S04 
-f-  S03,  and  is  a  powerful  reagent  for  some  purposes. 

Carbon  Bisulphide,  CS2. — Sulphur  forms  with  carbon  a 
compound  known  as  carbon  bisulphide,  which  has  the  com- 
position represented  by  the  formula  CS2.  It  is  made  by 
bringing  carbon  and  sulphur  together  at  high  tempera- 
tures. It  is  a  liquid  which  boils  at  47°.  That  it  dissolves 
sulphur  has  already  been  seen  (see  Experiments  9  and  111). 
It  also  dissolves  many  other  substances. 

Selenium  and  Tellurium  and  their  Compounds. — These 
elements  are  rarely  met  with.  In  general,  their  properties 
are  very  similar  to  those  of  sulphur,  and  they  form  com- 
pounds analogous  to  the  principal  compounds  of  sulphur. 
They  combine  with  hydrogen,  forming  gases  which  have 
bad  odors — much  worse  than  that  of  hydrogen  sulphide. 
They  burn  in  oxygen,  forming  oxides,  Se02  and  Te02. 
Corresponding  to  these  oxides  there  are  acids,  H2Se03  and 
H2Te03,  the  analogues  of  sulphurous  acid,  and  HaSe04  and 


264  INTRODUCTION  TO  CHEMISTRY. 

H3Te04,  the  analogues  of  sulphuric  acid.     The  compounds 
with  hydrogen  are  less  stable  than  hydrogen  sulphide. 

The  atomic  weights  of  the  three  elements  of  the  sulphur 
family  bear  a  simple  relation  to  one  another,  like  that 
already  noticed  between  the  atomic  weights  of  the  members 
of  the  bromine  family.  We  have  sulphur,  32;  selenium, 
79;  tellurium,  125.  The  atomic  weight  of  selenium  is 
nearly  the  mean  'of  the  atomic  weights  of  sulphur  and 
tellurium: 


Points  of  Resemblance  between  Oxygen  and  the  Members 
of  the  Sulphur  Family.  —  Between  the  elements  oxygen  and 
sulphur  there  is  very  little  resemblance,  but  the  compounds 
of  the  two  elements  present  many  points  of  analogy.  This 
is  seen  particularly  in  the  compounds  which  they  form  with 
hydrogen  and  with  the  metals.  Water  and  hydrogen  sul- 
phide are  analogous  in  composition  and  in  their  decompo- 
sitions. This  is  also  markedly  true  of  the  metallic  oxides 
and  sulphides;  and  of  the  hydroxides  and  hydrosulphides. 
On  the  other  hand,  oxygen  is  unique  in  many  respects, 
and  is  certainly  not  nearly  so  closely  related  to  sulphur  as 
selenium  and  tellurium  are. 


CHAPTER  XV. 
i 

THE    NITROGEN    FAMILY:    NITROGEN,     PHOSPHORUS, 
ARSENIC,  AND  ANTIMONY. 

BETWEEN  the  element  nitrogen  and  the  other  elements 
which  are  included  in  this  family  there  is  but  little  resem- 
blance. Nitrogen,  as  we  have  seen,  is  a  very  inactive  ele- 
ment. Phosphorus,  on  the  other  hand,  is  one  of  the 
most  active.  Nitrogen  does  not  combine  directly  with 
oxygen.  Phosphorus  combines  with  oxygen  even  at  ordi- 
nary temperatures,  while  at  the  burning  temperature  the 
combination  takes  place  violently.  The  elements  arsenic 
and  antimony  resemble  each  other  in  many  respects,  and 
are  also  allied  to  phosphorus.  On  studying  the  compounds 
which  all  the  members  of  the  family  form,  we  recognize 
clearly  that  they  are  closely  related. 

Phosphorus,  P  (At.  Wt.  31). — This  element  occurs  in 
nature  in  the  form  of  phosphates,  or  salts  of  phosphoric 
acid.  The  chief  of  these  is  calcium  phosphate,  which  is 
the  principal  constituent  of  the  minerals  phosphorite  and 
apatite  and  of  the  ashes  of  bones. 

It  is  prepared  from  bone-ash.  This  is  first  treated  with 
sulphuric  acid.  The  acid  converts  it  into  a  compound, 
which,  when  mixed  with  charcoal  and  heated,  is  reduced, 
yielding  free  phosphorus.  The  phosphorus  thus  obtained 
is  cast  into  sticks  under  water,  and  preserved  under  water. 

It  is  colorless  or  slightly  yellow  and  translucent.     At  or- 


266  INTRODUCTION  TO  CHEMISTRY. 

dinary  temperatures  it  can  be  cut  like  wax,  but  it  becomes 
hard  and  brittle  at  lower  temperatures.  It  melts  at  a  low 
temperature  (44°)  and  boils  at  290°.  Unless  carefully 
protected  from  the  light,  its  appearance  changes.  It  be- 
comes opaque  and  darker  in  color,  and  finally  dark  red. 
This  change  can  be  hastened  by  heating  the  phosphorus  in 
a  sealed  tube  to  a  temperature  of  about  250°. 

It  is  insoluble  in  water,  but  soluble  in  carbon  bisulphide. 
In  contact  with  the  air  it  gives  off  fumes  which  emit  a  pale 
light  visible  in  a  dark  room.  It  takes  fire  when  rubbed  or 
cut,  and  must  hence  be  handled  with  great  care.  It  should 
always  be  cut  under  water,  and  never  held  in  the  hand. 
It  not  only  combines  with  oxygen  easily,  but  with  other 
elements,  such  as  chlorine,  bromine,  and  iodine,  the  action 
in  each  case  being  accompanied  by  an  evolution  of  heat  and 
light.  The  combination  of  phosphorus  with  oxygen  has 
already  been  seen.  Its  conduct  towards  iodine  can  be 
shown  by  a  very  simple  experiment. 

EXPERIMENT  117. — Bring  together  in  a  porcelain  cruci- 
ble or  evaporating-dish  a  little  phosphorus  and  iodine.  It 
will  be  seen  that  simple  contact  is  sufficient  to  cause  the 
two  substances  to  act  upon  each  other.  Direct  combina- 
tion takes  place,  and  the  action  is  accompanied  by  light 
and  heat. 

Phosphorus  is  very  poisonous.  It  is  used  in  the  manu- 
facture of  matches. 

Red  Phosphorus. — The  red  substance  formed  when  ordi- 
nary phosphorus  is  left  in  the  light,  or  heated  without 
access  of  air,  is  a  second  variety  of  phosphorus  known  as 
red  phosphorus.  This  differs  from  ordinary  phosphorus  as 
much  as  graphite  differs  from  the  diamond.  Ordinary 
phosphorus  is  very  active,  combining  readily  with  oxy- 


PHOSPHINE. 

gen;  it  is  soluble  in  carbon  bisulphide;  and  is  poison- 
ous. Ked  phosphorus,  on  the  other  hand,  is  inactive.  It 
does  not  change  in  the  air,  and  requires  to  be  heated  to  a 
comparatively  high  temperature  before  it  will  combine 
with  oxygen;  it  is  insoluble  in  carbon  bisulphide,  and  is 
not  poisonous.  Red  phosphorus  is  converted  into  the  ordi- 
nary variety  by  heating  it  to  about  300°. 

The  cause  of  the  great  difference  in  the  properties  of 
the  two  varieties  of  phosphorus  is  not  known. 

There  are  some  other  modifications  of  phosphorus,  but 
they  are  rarely  met  with. 

Phosphine,  Phosphuretted  Hydrogen,  PH3. — The  chief 
compound  of  phosphorus  and  hydrogen  is  phosphine,  PH3. 
It  is  made  by  dissolving  phosphorus  in  caustic  potash  or 
soda.  The  reaction  which  takes  fplace  is  not  altogether 
simple,  and  need  not  be  explained- at  present.  The  points 
of  cl^ief  interest  in  regard  to  the  substance  are:  (1)  its  com- 
position, PH3,  which  is  analogous  to  that  of  ammonia,  NH3; 
(2)  its  power  to  combine  with  some  acids  as  ammonia  does, 
forming  unstable  phosphonium  salts  analogous  to  the  am- 
monium salts;  and  (3)  its  power  to  take  fire  when  brought 
in  contact  with  the  air. 

It  has  a  disagreeable  odor. 

EXPERIMENT  118. — Arrange  an  apparatus  as  shown  in  Fig. 
48.  In  the  flusk  B  put  about  5  grams  caustic  potash,  dissolved 
in  10-15  cc.  water,  and  add  a  few  small  pieces  of  phosphorus 
the  size  of  a  pea.  Pass  hydrogen  for  some  time  through 
the  apparatus  from  the  generating-flask  A  until  all  the  air 
is  displaced;  then  disconnect  at  D,  leaving  the  rubber  tube, 
closed  by  the  pinch-cock,  on  the  tube  which  enters  the  flask. 
Gently  heat  the  contents  of  the  retort,  when  gradually  a  gas 
will  be  evolved  and  escape  through  the  water  in  C.  As  each 


268 


INTRODUCTION  TO  CHEMISTRY. 


bubble  comes  in  contact  with  the  air  it  takes  fire,  and  the 
products  of  combustion  arrange  themselves  in  rings  which 
become  larger  as  they  rise.  They  are  extremely  beautiful, 
particularly  if  the  air  of  the  room  is  quiet.  Both  the 


FIG.  48. 

phosphorus  and  the  hydrogen  combine  with  oxygen  in  the 
act  of  burning. 

The  spontaneous  inflammability  of  phosphine  has  been 
found  to  be  due  to  the  presence  of  a  small  quantity  of 
another  compound  of  phosphorus  and  hydrogen  which  is 
formed  by  the  action  of  phosphorus  on  caustic  potash. 

Compounds  of  Phosphorus  with  Oxygen  and  with  Hydro- 
gen and  Oxygen. — The  product  formed  by  the  combina- 
tion of  phosphorus  and  oxygen  has  the  composition  ex- 
pressed by  the  formula  P006.  This  combines  with  water 
in  different  proportions,  forming  two  distinct  acids,  known 
as  metaphosphoric  and  orthophosphoric  acids : 

Pa06  +  H30    =          2HPO,, 

Metaphosphoric  acid» 
Orthophosphoric  acid. 


PHOSPHORIC  ACIDS.  269 

Orthophosphoric  or  ordinary  phosphoric  acid,  H3P04,  is 

the  principal  compound  of  phosphorus.  It  is  the  final 
product  of  the  action  of  air  and  moisture  on  phosphorus. 
As  has  been  stated,  it  occurs  in  nature  as  the  calcium  salt 
in  phosporite  and  apatite.  This  salt  is  also  the  chief  con- 
stituent of  bone-ash. 

It  can  be  made  by  treating  bone-ash  with  sulphuric  acid, 
or  by  oxidizing  phosphorus. 

It  is  a  solid  crystallized  substance. 

Phosphoric  acid  has  the  power  of  forming  three  distinct 
salts  with  the  same  metal.  It  is  hence  called  tribasic. 
With  sodium,  for  example,  it  forms  the  three  salts  Na3P04, 
Na2HP04,  and  NaH2P04.  Its  normal  calcium  salt — that  is 
to  say,  the  one  in  which  all  the  three  acid  hydrogen  atoms 
are  replaced  by  calcium — has  the  formula  Ca3(P04)a,  three 
bivalent  calcium  atoms  replacing  six  atoms  of  hydrogen. 

[Write  the  equation  expressing  the  action  which  takes 
place  when  sulphuric  acid  decomposes  normal  calcium 
phosphate,  forming  calcium  sulphate  and  phosphoric  acid.] 

When  phosphoric  acid  is  heated  to  a  sufficiently  high 
temperature,  it  loses  hydrogen  and  oxygen  in  the  form  of 
water  and  yields  metapliosphoric  acid : 

H3P04  =  HP03  +  H20. 

Metaphosphoric  acid  is  the  substance  found  in  com- 
merce under  the  name  of  glacial  phosphoric  acid.  It  is 
made  by  evaporating  solutions  of  phosphoric  acid  down  to 
dryness  and  heating  the  residue. 

When  a  salt,  like  ordinary  sodium  phosphate,  KN"a2P04, 
is  heated,  it  loses  water  and  yields  a  salt  of  pyrophosphoric 
acid : 

Na4PaO,  +  H80. 


270  INTRODUCTION  TO  CHEMISTRY. 

It  will  thus  be  seen  that  ordinary  phosphoric  acid  by 
losing  water  yields  pyrophosphoric  acid,  H4Pa07,  and 
metaphosphoric  acid,  HP03.  Both  these  acids  take  up 
water  and  are  reconverted  into  ordinary  phosphoric  acid  : 

HP03  +  H20  =  H3P04,  and 


Phosphorous  Acid,  H3P03.—  This  acid  is  formed  by  allow- 
ing moist  air  to  act  on  phosphorus.  There  is  an  oxide, 
Pa08,  which  bears  to  the  acid  the  same  relation  that  phos- 
phorus pentoxide  bears  to  phosphoric  acid  : 


PA  +  3H20  =  2H3P03. 

Arsenic  and  its  Compounds.  —  Arsenic*  occurs  in  nature  in 
combination  with  metals  —  as,  for  example,  iron,  copper, 
cobalt,  nickel,  etc.  —  and  in  combination  with  oxygen,  as  the 
trioxide  As209. 

It  is  generally  obtained  by  heating  arsenical  pyrites, 
FeAsS,  when  the  arsenic  separates  from  the  iron  and 
sulphur  : 

FeAsS  =  FeS  +  As. 

It  is  also  made  by  reducing  arsenic  trioxide  : 

As203  +  30  =  300  +  2As. 

It  has  a  metallic  lustre.  When  heated  to  quite  a  high 
temperature  in  the  air  it  takes  fire,  and  burns  with  a  bluish 
flame,  giving  off  a  smoke  which  has  the  odor  of  garlic  and 
is  poisonous. 

*  Symbol,  As.     At.  wt.  75. 


AR8INE. 


271 


It  combines  directly  with  most  elements.  In  the  ele- 
mentary form  it  is  not  poisonous,  but  when  oxidized  it 
becomes  so. 

Arsine,  Arseniuretted  Hydrogen,  AsH3. — This  compound 
is  analogous  to  ammonia  and  phosphine.  It  is  made  by 
the  action  of  nascent  hydrogen  [what  is  nascent  hydrogen?] 
on  the  compounds  of  arsenic  with  oxygen,  as  when  these 
compounds  are  brought  into  a  vessel  containing  zinc  and 
sulphuric  acid. 

EXPERIMENT  119. — Arrange  an  apparatus  as  shown  in 
Fig.  49.  Put  some  granulated  zinc  in  the  Wolff  flask  and 


FIG.  49. 

pour  dilute  sulphuric  acid  on  it.     When  the  air 
of  the  vessel  and  the  hydrogen  is  lighted,  add 
little  of  a  solution  of    arsenic   trioxide,  As203, 
hydrochloric  acid.     The  appearance  of  the  flame 
change,  becoming  paler,  with  a  slightly  bluish 
giving  off  white  fumes.     (See  Experiment  120.) 

Arsine  is  a  colorless  gas.     It  is  very  poisonous 
an  unpleasant  odor.     When  lighted  it  burns  with 


is  all  out 
slowly  a 
in  dilute 
will  soon 
tint,  and 

and  has 
a  bluish- 


272.'  INTRODUCTION  TO  CHEMISTRY. 

white  flame,  forming  arsenic  trioxide  and  water.  It  is  very 
unstable,  breaking  up  into  arsenic  and  hydrogen  when 
heated.  When  a  cold  object,  as  a  piece  of  porcelain,  is 
brought  into  the  flame  of  burning  arsine,  the  arsenic  is 
deposited  in  the  form  of  a  dark  spot.  This  fact  is  taken 
advantage  of  for  the  purpose  of  detecting  the  presence  of 
arsenic.  It  is  extensively  used  in  examining  the  stomach 
and  other  viscera  of  human  beings  in  cases  of  suspected 
poisoning.  It  is  known  as  Marsh's  test,  having  been  in- 
troduced by  a  chemist  by  the  name  of  Marsh. 

EXPERIMENT  120. — Into  the  flame  of  the  burning  hy- 
drogen and  arsine  produced  in  the  last  experiment  intro- 
duce a  piece  of  porcelain,  as  the  bottom  of  a  small  porcelain 
dish  or  a  crucible,  and  notice  the  appearance  of  the  spots. 
Heat  by  means  of  a  Bunseu  burner  the  tube  through  which 
the  gas  is  passing,  which  should  be  of  hard  glass.  Just  in 
front  of  the  heated  place  there  will  be  deposited  a  thin 
layer  of  metallic  arsenic,  commonly  called  a  mirror  of 
arsenic.  This  deposit  is  due  to  the  direct  decomposition  of 
the  arsine  into  arsenic  and  hydrogen  by  heat.  [Compare 
ammonia,  phosphine,  and  arsine  with  reference  to  their 
stability.] 

Arsine  has  no  basic  properties,  differing  markedly  in 
this  respect  from  ammonia.  Phosphine,  as  has  been  stated, 
has  weak  basic  properties. 

Arsenic  Trioxide,  As203.— When  arsenic  is  burned  in  the 
air  or  in  oxygen  it  forms  the  trioxide.  [Compare  with 
phosphorus  in  this  respect.]  This  substance,  which  is 
generally  called  arsenic,  is  made  by  heating  compounds  of 
arsenic  and  metals  in  contact  with  the  air.  Under  these 
circumstances,  both  the  metal  and  the  arsenic  are  oxidized, 
and  the  oxide  of  arsenic,  being  volatile,  passes  off  and  is 


ANTIMONY.  273 

condensed  and  collected  in  large  chambers  of  mason- 
work. 

It  is  a  colorless,  amorphous,  glassy  mass.  It  is  difficultly 
soluble  in  water,  more  easily  in  hydrochoric  acid.  It  has 
a  weak,  disagreeably  sweet  taste,  and  acts  very  poisonously. 
It  is  probably  more  frequently  used  as  a  poison  than  any 
other  substance.  Minute  quantities  can  be  detected  by  the 
chemist  with  absolute  certainty. 

The  oxide  is  easily  reduced  by  means  of  carbon. 

EXPERIMENT  121. — Mix  together  about  equal  small 
quantities  of  arsenic  trioxide  and  finely  powdered  char- 
coal. Heat  the  mixture  in  a  small  dry  tube  of  hard  glass, 
closed  at  one  end.  The  arsenic  which  is  set  free  will  be 
deposited  on  the  walls  of  the  tube  in  the  form  of  a  mirror, 
like  that  obtained  in  Experiment  120. 

Arsenic  forms  with  oxygen  and  hydrogen  an  acid  of  the 
formula  H3As04,  known  as  arsenic  acid,  which  is 
analogous  to  orthophosphoric  acid.  When  heated,  it  un- 
dergoes changes  similar  to  those  considered  in  connection 
with  phosphoric  acid,  the  products  being  metarsenic  acid, 
HAs03,  and  pyroarsenic  acid,  H4As207. 

When  arsenic  trioxide  is  treated  with  bases  in  solution, 
salts  of  arsenious  acid,  or  the  arsenites,  are  formed.  The 
formula  of  the  potassium  salt  is  K3As03.  The  acid 
H3As03  diifers  from  arsenic  acid,  H3As04,  by  one  atom  of 
oxygen  in  the  molecule. 

Antimony*  occurs  most  frequently  in  combination  with 
sulphur  as  the  sulphide  Sb2S3.  It  is  a  silver- white, 
metallic-looking  substance.  At  ordinary  temperature  it 
is  not  changed  by  contact  with  the  air;  but  when  heated  to 

*  Symbol,  Sb.     At,  wt.  120. 
18 


274  INTRODUCTION  TO  CHEMISTRY. 

a  sufficiently  high  temperature  in  the  air  it  takes  fire  and 
burns,  forming  the  white  oxide. 

EXPERIMENT  122. — Heat  a  small  piece  of  antimony  on 
charcoal  by  means  of  the  blow-pipe.  Notice  the  formation 
of  the  white  coating  on  the  charcoal  around  the  place  where 
the  substance  burned.  [What  difference  is  there  between 
the  conduct  of  antimony  and  arsenic  before  the  blow-pipe?] 
It  would  be  well  for  the  teacher  to  give  the  student  a  small 
piece  of  arsenic  and  another  of  antimony,  and  ask  him  to 
determine  by  means  of  the  blow-pipe  which  is  the  arsenic 
and  which  is  the  antimony. 

Stibine,  Antimoniuretted  Hydrogen,  SbH3. — This  com- 
pound is  made  by  the  same  method  as  that  described  under 
arsine. 

EXPERIMENT  123. — Make  some  stibine,  using  a  solution 
of  tartar  emetic  which  contains  antimony. 

Its  properties  are  very  much  like  those  of  arsine.  It 
burns  with  a  similar  flame  and  is  decomposed  in  the  same 
way. 

EXPERIMENT  124. — Introduce  a  piece  of  porcelain  in  the 
flame  and  notice  the  deposit  or  antimony  spot.  It  is 
darker  and  more  smoky  than  the  arsenic  spot.  There  are 
other  differences  in  properties,  but  they  need  not  be  con- 
sidered here. 

Antimony  forms  acids  resembling  phosphoric,  metaphos- 
phoric,  and  pyrophosphoric  acids. 

Antimony  as  a  Base-forming  Element. — Antimony  not 
only  forms  acids  with  hydrogen  and  oxygen,  but  it  also 
forms  bases.  These  bases  neutralize  acids  and  form  salts 
in  which  the  hydrogen  of  the  acids  is  replaced  by  antimony. 
Some  of  these  salts  are  rather  complicated  in  composition, 
and  it  would  lead  too  far  to  discuss  them  here.  It  is  suffi- 


NITROGEN  FAMILY.  275 

cient  for  our  present  purpose  to  recognize  the  important 
fact  that  one  and  the  same  element  has  the  power  to  form 
acids  and  bases. 

Antimony,  however,  is  not  the  only  element  thus  far 
considered  which  has  this  double  power.  The  compounds 
of  nitrogen  with  hydrogen  and  oxygen  have,  in  general, 
acid  properties,  but  ammonia  has  strongly  basic  properties. 
We  see,  therefore,  that  when  nitrogen  is  combined  with 
hydrogen  the  product  has  basic  properties,  while  when 
combined  with  hydrogen  and  oxygen  in  forms  in  which 
the  oxygen  is  in  excess  the  products  are  acids.  The  same 
is  true  to  a  slight  extent  of  phosphorus. 

At  the  same  time,  neither  the  element  nitrogen  nor  the 
element  phosphorus  itself  has  the  power  to  replace  the 
hydrogen  of  acids,  and  this  power  antimony  has. 

There  are  three  rare  elements  which  in  their  chemical 
conduct  resemble  the  members  of  the  nitrogen  family. 
These  are  vanadium,  colunibium,  and  tantalum.  It  would 
be  unprofitable  to  undertake  their  study  at  this  stage. 

General  Remarks  on  the  Characteristics  of  the  Nitrogen 
Family. — The  resemblance  between  nitrogen  and  phos- 
phorus is  seen  particularly  in  the  compounds  ammonia  and 
phosphine.  Between  the  oxides  of  nitrogen  and  of  phos- 
phorus the  resemblance  is  not  striking.  There  are  two 
oxides  of  nitrogen, — the  trioxide,  N203,  and  the  pentoxide, 
N205,  which  in  composition  correspond  to  the  two  oxides 
of  phosphorus,  Pa03  and  P206.  But  while  the  pentoxide 
of  phosphorus  is  the  most  common  oxide  of  this  element, 
the  pentoxide  of  nitrogen  is  obtained  with  greater  difficulty 
than  any  of  the  other  oxides  of  nitrogen.  There  are  no 
compounds  of  phosphorus  analogous  to  the  three  principal, 
oxides  of  nitrogen, — nitrous  oxide,  N20;  nitric  oxide,  NO, 


276  INTRODUCTION  TO  CHEMISTRY. 

and  nitrogen  peroxide,  N02.  There  is  no  acid  of  phos- 
phorus corresponding  to  nitrous  acid,  HN02,  and  there  are 
no  compounds  of  nitrogen  analogous  to  phosphoric?  acid, 
H3P04,  and  pyrophosphoric  acid,  H4P207.  Nitric  acid, 
HN03,  and  metaphosphoric  acid,  HP03,  have  analogous 
compositions. 

The  resemblance  between  phosphorus,  arsenic,  and  anti- 
mony is  much  more  striking  than  that  between  nitrogen 
and  phosphorus.  This  resemblance  has  already  been 
noticed  in  the  acids  formed  by  the  three  elements,  and  in 
their  hydrogen  compounds,  PH3,  AsH3,  and  SbH3,  all  of 
which  are  analogous  to  ammonia.  The  same  resemblance 
is  seen  in  their  oxides,  P203,  P206,  As203,  As,06,  and  Sb303, 
Sb20B.  Their  compounds  with  chlorine  and  the  other 
members  of  the  chlorine  family  are  also  strikingly  similar. 

The  elements  of  the  nitrogen  family  are  trivalent  in 
some  compounds,  as  in  NH3,  PH3,  AsH3,  PC1S,  As013,  etc.; 
and  quinquivalent  in  others,  as  in  NH4C1,  in  which  the 
nitrogen  is  believed  to  hold  in  combination  four  atoms  of 
hydrogen  and  one  atom  of  chlorine;  in  P015,  etc.,  etc. 

The  atomic  weights  are  N  =  14;  P  =  31;  As  =  75;  Sb  = 
120.  These  figures  do  not  all  bear  simple  relations  to  one 
another,  but  between  the  atomic  weights  of  phosphorus, 
arsenic,  and  antimony  there  exists  a  relation  similar  to 
that  already  noticed  between  the  atomic  weights  of  chlorine, 
bromine,  and  iodine,  and  sulphur,  selenium,  and  tellurium. 
We  have  P  =  31,  Sb  =  120,  and  As  =  75: 

31  +  120 
-- £—     -  75.5. 

Boron,  B  (At.  Wt.  10.9). — Boron  may  conveniently  be 
considered  in  connection  with  the  nitrogen  family,  as  some 


BORON.  277 

of  its  properties  suggest  those  of  the  members  of  the  family. 
At  the  same  time,  it  presents  peculiarities  which  distinguish 
it  from  these  elements.  Boron  occurs  in  nature  in  the 
form  of  boric  acid,  or  as  salts  of  this  acid,  particularly  the 
sodium  salt,  or  borax.  It  is  prepared  by  treating  the  oxide, 
B203,  at  a  very  high  temperature  with  sodium  or  alumin- 
ium. Under  proper  conditions  it  is  obtained  in  the  form 
of  crystals  which  are  almost  as  hard  as  diamonds. 

At  a  red  heat  uncrystallized  boron  combines  with  nitro- 
gen very  readily.  The  crystallized  variety  can  be  heated 
to  a  high  temperature  in  the  air  without  changing.  These 
properties  distinguish  boron  from  the  members  of  the 
nitrogen  family,  all  of  which,  with  the  exception  of  nitro- 
gen, combine  with  oxygen.  Boron  combines  with  chlorine, 
forming  the  chloride  BC13,  analogous  to  the  chlorides  of 
phosphorus  and  arsenic,  PCI3  and  AsCl3. 

Boric  Acid,  H3B03, — The  chief  compound  of  boron  is 
boric  acid.  It  occurs  in  nature  in  large  quantities,  issuing 
from  the  earth  with  Avater  vapor  in  some  localities,  partic-' 
ularly  in  Tuscany.  The  jets  of  steam  charged  with  boric 
acid,  which  are  called  suffioni,  are  conducted  into  tanks  of 
water,  in  which  the  acid  condenses.  The  solution  is 
evaporated  by  means  of  the  heat  of  the  natural  steam-jets, 
and  finally  the  acid  crystallizes  out.  The  acid  is  also 
obtained  from  a  natural  magnesium  salt  called  boracite, 
and  from  borax,  which  is  a  sodium  salt. 

When  heated  to  100°,  boric  acid  loses  water  and  is  con- 
verted into  metaboric  acid,  HB02: 

H3B03  =  HB02  +  H20. 
[What  is  the  analogous  change  of  phosphoric  acid?] 


278  INTRODUCTION  TO  CHEMISTRY. 

The  acid  thus  obtained  is  analogous  to  nitrous  acid  in 
composition. 

When  heated  higher,,  a  larger  proportion  of  water  is 
given  off,  and  an  acid  of  the  formula  H2B407,  or  tetrdboric 
acid,  is  left  behind.  This  is  the  form  of  boric  acid  from 
which  borax  is  derived.  The  formula  of  borax  is  Na,B407 
-f  10H20.  The  relation  between  tetraboric  acid  and  nor- 
mal boric  acid  is  shown  by  the  equation 

4H3B03  =  H2B407  +  5H20. 

Heated  to  a  still  higher  temperature,  boric  acid  loses  all 
its  hydrogen  in  the  form  of  water,  and  leaves  behind  boron 
trioxide,  or  boric  anhydride,  B208.  [What  is  the  signifi- 
cance of  the  name  boric  anhydride?] 

When  a  solution  of  borax  is  treated  with  sulphuric  acid, 
boric  acid  is  set  free,  and  crystallizes  out  if  the  solution  is 
concentrated  enough. 

EXPERIMENT  125.— Make  a  hot  solution  of  30  grams 
crystallized  borax  in  120  cc.  water.  Add  slowly  10  grams 
concentrated  sulphuric  acid.  On  cooling,  the  boric  acid 
will  crystallize  out.  [What  evidence  have  you  that  the  sub- 
stance which  crystallizes  out  of  the  solution  is  not  borax?] 
Try  the  solubility  in  alcohol  of  specimens  of  each.  [Is  there 
any  difference?]  Treat  a  few  crystals  of  borax  with  about 
10  cc.  alcohol;  pour  off  the  alcohol  and  set  fire  to  it.  Treat 
a  few  crystals  of  the  boric  acid  in  the  same  way.  [What 
difference  do  you  observe?] 

Boric  Anhydride,  B203,  when  heated,  melts  and  forms  a 
clear  glass.  This  has  the  power  to  dissolve  many  sub- 
stances which  ordinary  solvents  will  not  dissolve,  and  some 
of  the  solutions  thus  formed  are  colored.  This  fact  is 
taken  advantage  of  in  the  laboratory  for  the  purpose  of 


BORON.  279 

detecting  the  presence  of  those  substances  which  form  col- 
ored solutions.  The  method  of  work  consists  in  melting  a 
little  boric  acid  or  borax  in  a  loop  of  platinum  wire,  and 
then  bringing  a  minute  particle  of  the  substance  to  be  ex- 
amined in  contact  with  the  glass  bead  thus  formed.  When 
heated  before  the  blow-pipe  it  will  generally  dissolve.  By 
holding  the  bead  in  the  oxidizing  flame  of  the  blow-pipe 
the  substance  in  solution  is  frequently  oxidized,  and  by 
holding  it  in  the  reducing  flame  it  is  frequently  reduced. 
Changes  of  color  may  thus  be  produced  which  will  aid  us 
in  determining  what  substance  we  have  to  deal  with.  This 
method  is  valuable  for  the  purposes  of  analysis. 

When  an  alcoholic  solution  of  boric  acid  is  lighted,  it 
burns  with  a  green  flame.  The  salts  of  boric  acid  do  not 
color  the  alcohol  flame.  [What  evidence  have  you  had  of 
the  truth  of  this  statement?] 

Boron  is  trivalent  in  most  of  its  compounds,  as  in  the 
chloride,  BC13. 


CHAPTER  XVI. 
THE  CARBON  FAMILY:  CARBON  AND  SILICON. 

Silicon,  Si  (At.  Wt.  28).— We  have  already  learned  Low 
important  a  r61e  carbon  plays  in  animate  nature.  It  is 
interesting  to  note  that  silicon,  which  in  some  respects  re- 
sembles carbon  from  a  chemical  standpoint,  is  one  of  the 
most  important  constituents  of  the  mineral  or  inorganic 
parts  of  the  earth.  It  occurs  chiefly  in  the  form  of  the 
oxide,  Si02,  commonly  called  silica,  or  silicon  dioxide;  and 
in  combination  with  oxygen  and  several  of  the  common 
metals,  particularly  with  sodium,  potassium,  aluminium, 
and  calcium,  in  the  form  of  the  silicates.  Next  to  oxygen> 
silicon  is  the  most  abundant  element  in  nature.  There  are 
extensive  mountain-ranges  consisting  almost  entirely  of 
silicon  dioxide,  Si02,  in  the  form  known  as  quartz  or 
quartzite.  Other  ranges  are  made  up  of  silicates,  which 
are  compounds  formed  by  a  combination  of  silicon  dioxide 
and  bases.  The  clay  of  valleys,  river-beds,  etc. ,  also  con- 
tains silicon  in  large  quantity,  while  the  sand  found  so 
abundantly  at  the  sea-shore  is  mostly  silicon  dioxide,  Si02. 

Silicon  is  never  found  in  the  free  state,  and  it  is  an  ex- 
tremely difficult  thing  to  decompose  the  oxide,  Si02,  in 
such  a  way  as  to  get  the  element,  though  it  can  be  accom- 
plished by  heating  the  oxide  with  potassium.  Under 
proper  conditions  silicon  can  be  obtained  in  the  form  of 
crystals  which  have  a  gray  color  and  are  harder  than 


SILICIC  ACID.  281 

glass.     It  is  not  acted  upon  by  the  strongest  acids,  nor  when 
heated  in  a  current  of  oxygen. 

With  hydrogen  silicon  forms  a  gaseous  compound  of  the 
formula  SiH4;  it  combines  with  chlorine,  forming  SiCl4, 
and  with  fluorine,  forming  SiF4.  The  fluoride  has  already 
been  referred  to  in  connection  with  the  action  of  hydro= 
fluoric  acid  on  silicates.  We  have  seen  that  hydrofluoric 
acid  dissolves  silicates — as,  for  example,  glass — in  conse- 
quence of  the  action  of  the  acid  on  silicon  dioxide,  which 
is  represented  thus: 

Si02  +  4HF  =  SiF4  +  2H20. 

The  silicon  fluoride  passes  off  in  the  form  of  gas. 

Silicic  Acid. — There  are  several  varieties  of  silicic  acid, 
all  of  which  are,  however,  derived  from  an  acid  of  the 
formula  H4Si04,  or  normal  silicic  acid.  When  this  is  set 
free  from  its  salts,  it  loses  water,  and  is  changed  to 
ordinary  silicic  acid,  H2Si03: 

H4Si04  =  H.SiO,  +  H30. 

When  heated,  this  second  Torm  of  silicic  acid  is  con- 
verted into  the  dioxide  Si02: 

H2S503  =  Si02  +  H20. 

Most  of  the  ordinary  silicates  are  derived  from  the  acid 
of  the  formula  H2Si03.  [What  is  the  formula  of  carbonic 
acid?  Under  what  circumstances  does  carbonic  acid  break 
up  into  carbon  dioxide  and  water?]  Other  silicic  acids  are 
obtained  by  heating  ordinary  silicic  acid.  Thus,  under  the 
proper  conditions  an  acid  of  the  formula  H2Si20B,  and  one 
of  the  formula  H4Si308,  can  be  obtained: 

2H2Si03  =  H.Si.O.  +  HaO; 
3HaSi03  =  H4Sia08  +  H20. 


282  INTRODUCTION  TO  CHEMISTRY. 

These  are  called  polysilicic  acids.  Some  of  these  are 
found  in  nature.  Opal  is  the  best  known  example. 

Silicon  Dioxide,  Silicic  Anhydride,  Si02.  —  As  already 
stated,  this  substance  occurs  very  abundantly  in  nature  and 
in  many  different  forms.  Quartz,  or  rock  crystal,  is  pure 
crystallized  silicon  dioxide;  quartzite  is  a  coarser-grained 
substance  made  up  of  small  crystals  of  quartz,  usually  col- 
ored. Agate,  amethyst,  and  carnelian  are  varieties  of 
quartz  colored  by  foreign  substances. 

Silicon  dioxide  is  insoluble  in  water  and  acids.  It  is  solu- 
ble in  hydrofluoric  acid,  as  has  been  stated.  Glass  is  made 
up  of  salts  of  silicic  acid,  usually  of  the  sodium  or  potas- 
sium salts  and  calcium  salts. 

Comparison  of  Carbon  and  Silicon.— The  two  elements  of 
this  family  resemble  each  other  in  the  composition  of  some 
of  their  simplest  compounds,  as  carbon  dioxide,  C02,  and 
silicon  dioxide,  Si02;  carbonic  acid,  H2C03,  and  silicic  acid, 
H2Si03;  marsh  gas,  CH4,  and  silicon  hydride,  SiH4;  carbon 
tetrachloride,  CC14,  and  silicon  tetrachloride,  SiCl4.  On 
the  other  hand,  they  present^marked  points  of  difference. 
Each  yields  a  large  number  of  derivatives,  but  the  deriva- 
tives of  carbon  bear  to  the  element  relations  entirely  differ- 
ent from  those  which  the  derivatives  of  silicon  bear  to  this 
element.  The  compounds  of  carbon  can  all  be  shown  to 
be  derived  from  the  hydrocarbons;  that  is  to  say,  they  may 
be  regarded  as  formed  from  the  hydrocarbons  by  a  com- 
paratively simple  set  of  changes  [what  are  the  hydrocar- 
bons?], while  most  of  the  compounds  containing  silicon 
are  derivatives  of  silicic  acid. 


CHAPTER  XVII. 

BASE-FORMING  ELEMENTS.— GENERAL  CONSIDERA- 
TIONS. 

AT  the  end  of  Chapter  XII.  is  this  sentence:  "  After  the 
acid-forming  elements  have  been  considered,  the  base- 
formrng  elements  will  be  taken  up  in  a  similar  way;  but, 
as  will  be  seen,  the  chemistry  of  the  acid-forming  elements 
exhibits  more  variety,  and  is  hence  better  adapted  to  the 
illustration  of  the  general  principles  of  the  science  than 
that  of  the  base-forming  elements,  so  that  the  latter  need 
not  be  considered  as  fully/' 

The  significance  of  the  name  base-forming  elements  has 
been  stated.  It  is  simply  this:  that  the  compounds  of 
these  elements  with  hydrogen  and  oxygen  are  bases,  or,  in 
other  words,  have  the  power  to  neutralize  acids  and  form 
salts.  But  the  distinction  between  acid-forming  and  base- 
forming  elements  is  not  a  sharp  one,  for  the  reason  that 
there  are  some  elements  which  occupy  an  intermediate  posi- 
tion, forming  both  acids  and  bases.  One  example  of  this 
kind  already  considered  is  antimony,  and  the  reason  why 
it  was  considered  as  a  member  of  the  nitrogen  family  is 
that  it  is  unquestionably  closely  related  to  arsenic,  which  is 
strictly  an  acid-forming  element.  A  close  study  will  show 
that  those  elements  which  have  the  power  to  form  both 
acids  and  bases  are  related  to  one  of  the  four  families 
already  considered.  There  are,  thus,  certain  elements  which 


284  INTRODUCTION  TO  CHEMISTRY. 

show  some  resemblance  to  the  members  of  the  chlorine 
family,  but  nevertheless  act  principally  as  base-formers;  so, 
too,  there  are  certain  elements  which  resemble  the  mem- 
bers of  the  sulphur  family,  but  which  generally  form 
bases.  In  a  similar  way,  there  are  base-forming  analogues  of 
the  nitrogen  and  carbon  families.  Those  elements  which 
always  act  as  base-formers  .have  no  analogues  among  the 
acid-forming  elements. 

The  order  in  which  the  base-forming  elements  will  be 
taken  up  is  the  following: 

1.  The  Potassium  Family,  consisting  of  lithium,  sodi- 
um, potassium,  rubidium,  and  caesium. 

2.  The  Calcium  Family,  consisting  of  giucinum,  calcium, 
barium,  and  strontium. 

3.  The  Magnesium  Family,  consisting  of  magnesium, 
zinc,  and  cadmium. 

4.  The  Silver  Family,  consisting  of  silver,  copper,  and 
mercury. 

5.  The  Aluminium  Family,  of  which  aluminium  is  the 
only  well-known  member.     Allied   to  it  are  the  rare  ele- 
ments gallium,  indium,  thallium,  scandium,  yttrium,  lan- 
thanum, and  ytterbium. 

6.  The  Iron   Family,  consisting  of  iron,    cobalt,  and 
nickel. 

7.  The  Manganese  Family,  of  which  manganese  is  the 
only  representative.     There  are  some  points  of  resemblance 
between  manganese  and  the  members  of  the  chlorine  family. 

8.  The  Chromium  Family ,  consisting  of  chromium,  mo- 
lybdenum, and  tungsten.    The  members  of  this  family  show 
some  analogy  to  the  members  of  the  sulphur  family,  as  will 
be  pointed  out  when  chromium  is  considered. 

9.  The  Bismuth  Family,  of  which  bismuth  is  the  only 


METALLIC  PROPERTIES.  285 

representative.     There  are  some  points  of  resemblance  be- 
tween bismuth  and  the  members  of  the  nitrogen  family. 

10.  The  Lead  Family,  consisting  of  the  common  elements 
lead  and  tin,  and  the  rare  elements  titanium,  zirconium, 
cerium,  and  thorium. 

11.  The   Palladium  Family,  consisting  of    palladium, 
ruthenium,  and  rhodium. 

12.  The  Platinum  Family,  consisting  of  osmium,  irid- 
ium,  platinum,  and  gold. 

It  will  be  seen  at  once  that  there  are  many  more  base- 
forming  than  acid-forming  elements,  and  it  is  a  serious 
undertaking  to  become  thoroughly  acquainted  with  all  the 
elements  included  under  this  head.  In  order  to  get  a  gen- 
eral knowledge  of  the  principles  of  chemistry,  however,  it 
is  not  necessary  to  study  all  these  elements.  The  chemist 
must,  of  course,  familiarize  himself  to  some  extent  with 
all  of  them,  and  those  who  continue  the  study  of  chemistry 
hereafter  will  have  abundant  opportunity  to  study  them  in 
detail.  For  the  present  it  will  be  best  to  confine  our  at- 
tention to  a  few  of  the  representative  elements  included 
in  the  above  list.  A  knowledge  of  these  will  put  us  in  a 
position  to  study  the  others  without  serious  difficulty, 
should  occasion  demand. 

Metallic  Properties.  —  It  is  customary  to  divide  the 
chemical  elements  into  two  classes, — the  metals  and  the 
non-metals.  This  classification  was  originally  based  upon 
differences  in  the  physical  properties  of  the  elements,  the 
name  metal  being  applied  to  those  elements  which  have 
what  is  known  as  a  metallic  lustre,  are  opaque,  and  are 
good  conductors  of  heat  and  electricity.  All  those  elements 
which  do  not  have  these  properties  are  called  non-metals. 
Gradually  the  name  metal  came  to  signify  an  element  which 


286  INTRODUCTION  TO  CHEMISTRY. 

has  the  power  to  replace  the  hydrogen  of  acids  and  form 
salts,  and  the  name  non-metal  to  signify  an  element  which 
has  not  this  power.  This  classification  is  in  reality  about 
the  same  as  that  wnich  is  made  use  of  in  this  book.  It 
thus  appears  that,  in  general,  elements  which  have  similar 
physical  properties  have  also  similar  chemical  properties. 

Classes  of  Metal  Derivatives. — As  the  metals  or  base- 
forming  elements  all  combine  with  oxygen,  sulphur,  chlo- 
rine, and  hydrogen  and  oxygen,  and  also  form  salts  with  all 
acids,  it  follows  that  under  the  head  of  each  one  there  must 
be  a  large  number  of  compounds.  A  thorough  study  of 
each  metal  would  include  the  following  subjects  : 

1.  Its  Occurrence  in  Nature. — Under  this  head  we  would 
become  acquainted  with  those  natural  compounds  of  the 
metals  known  as  minerals.     Those  minerals  from  which  the 
metals   are    extracted   for  practical  purposes    are    called 
ores. 

2.  Extraction  of  the  Metals  from  their  Ores. — The  de- 
tailed study  of  this  subject  is  the  object  of  metallurgy. 

3.  The  Properties  of  Metals  as  such. — As  we  shall  find, 
metals  differ  very  markedly  from  one  another.     Some  are 
light,  floating  on  water,  as  lithium,  sodium,  etc.;  some  are 
extremely  heavy,  as  lead,  platinum,  etc.     Some   combine 
with  oxygen  with  great   energy;  others  form  very  wesik 
compounds  with  oxygen.     Some  form  strong  bases,  others 
form  weak  bases. 

4.  The  Compounds  of  the  Metals. — These  may  be  con- 
veniently classified  as  : 

a.  Compounds  with  chlorine,  bromine,  and  iodine;  or 
the  chlorides,  bromides,  and  iodides. 

It.  Compounds  with  oxygen  and  with  oxygen  and  hy- 
drogen; or  the  oxides  and  hydroxides. 


CLASSES  OF  COMPOUNDS.  287 

c.  Compounds  with  sulphur  and  with  sulphur  and  hy- 
drogen ;  or  the  sulphides  and  hydrosulphides. 

d.  Compounds  with  nitric  .and   nitrous  acids;  or  the 
nitrates  and  nitrites. 

e.  Compounds  with  the  acids  of  chlorine ;  or  the  chlo- 
rates, chlorites,  etc. 

/.  Compounds  with  sulphuric  and  sulphurous  acids  ;  or 
the  'sulphates  and  sulphites. 

g.  Compounds  with  carbonic  acid  ;  or  the  carbonates. 

h.  Compounds  with  phosphoric  acid  and  the  analogous 
acids  of  arsenic  and  antimony;  or  the  phosphates,  arsenates, 
etc. 

i.  Compounds  with  silicic  acid  ;  or  the  silicates. 

j.  Compounds  with  boric  acid  ;  or  the  borates. 

Of  the  almost  infinite  number  of  compounds  belonging 
to  the  classes  above  referred  to,  only  very  few  need  be 
studied  at  this  stage.  It  is  more  important  to  become  ac- 
quainted with  the  general  methods  of  preparation  and  the 
general  properties  of  these  compounds  than  to  learn  details 
in  regard  to  many  individual  members  of  each  class.  Only 
those  compounds  will  be  considered  which  well  illustrate 
general  principles,  or  which,  owing  to  some  familiar  ap~ 
'plication,  happen  to  be  of  special  interest. 

The  acids  of  which  the  salts  are  derivatives  are  already 
known  to  us,  and  in  dealing  with  the  acids  frequent  refer- 
ence has  been  made  to  the  methods  of  making  the  salts, 
and  to  some  of  their  more  important  properties.  It  will 
be  well,  before  taking  up  the  metals  systematically,  to  con- 
sider briefly  the  general  methods  of  preparation  and  the 
general  properties  of  the  different  classes  of  metallic  com- 
pounds. 

Chlorides  are   made   by   treating  a   metal  with   hydro- 


288  INTRODUCTION  TO  CHEMISTRY. 

chloric  acid  or  with  chlorine  ;  by  treating  an  oxide  or  a 
hydroxide  with  hydrochloric  acid  ;  by  treating  a  carbonate 
or  any  other  easily  decomposed  salt  with  hydrochloric  acid  ; 
by  adding  hydrochloric  acid  to  a  solution  containing  a 
metal  which  with  chlorine  forms  an  insoluble  compound. 

EXAMPLES. — Zinc  chloride  is  formed  by  treating  zinc 
with  hydrochloric  acid. 

[Write  the  equation.] 

Iron  chloride  is  formed  by  treating  iron  with  chlorine: 

Fe  +  301  =  FeCl3. 

Calcium  chloride  is  formed  by  treating  lime  or  calcium 
oxide,  CaO,  with  hydrochloric  acid  : 

CaO  +  2HC1  =  Ca012  +  H20. 

Sodium  chloride  is  formed  by  treating  sodium  hydroxide, 
or  caustic  soda,  NaOH,  with  hydrochloric  acid  : 

NaOH  +  HOI  =  NaCl  +  H20. 

[What  takes  place  when  caustic  soda  or  caustic  potash  is 
treated  with  chlorine  ?] 

Calcium  chloride  is  formed  when  calcium  carbonate* 
CaC03,  is  treated  with  hydrochloric  acid  : 

CaC03  +  2HC1  =  CaCl2  +  C02  +  H20. 

Silver  chloride  is  precipitated  when  hydrochloric  acid  or 
a  soluble  chloride  is  added  to  a  solution  containing  a  silver 
salt. 

EXPERIMENT  126. — Dissolve  a  small  crystal  of  silver 
nitrate  in  pure  water.  Add  to  a  small  quantity  of  this 


CHLORIDES.  289 

solution  in  a  test-tube  a  few  drops  of  dilute  hydrochloric 
acid.  The  white  substance  thus  precipitated  is  silver  chlo- 
ride, AgCl.  To  another  small  portion  of  the  solution  add  a 
few  drops  of  a  dilute  solution  of  common  salt,  or  sodium 
chloride,  NaCl.  The  white  substance  produced  in  this  case 
is  also  silver  chloride.  Add  ammonia  to  each  tube.  If  suffi- 
cient be  added  the  precipitates  will  dissolve.  On  adding 
enough  hydrochloric  acid  to  these  solutions  to  combine  with 
all  the  ammonia,  the  silver  chloride  is  again  thrown  down. 
On  standing  exposed  to  the  light  both  precipitates  change 
color,  becoming  finally  dark  violet.  The  reactions  involved 
in  the  above  experiments  are  these  :  In  the  first  place,  when 
hydrochloric  acid  is  added  to  silver  nitrate  this  reaction 
takes  place  : 

AgN03  -f  HC1  =  AgCl  +  HNO,. 
When  sodium  chloride  is  added  this  reaction  takes  place: 
AgN03  +  JSTaOl  =  AgCl  +  NaNO,. 

In  the  first  reaction  nitric  acid  is  set  free;  in  the  second, 
the  sodium  and  silver  exchange  places.  In  addition  to  the 
insoluble  silver  chloride,  there  is  formed  at  the  same  time 
the  soluble  salt,  sodium  nitrate.  On  adding  ammonia  the 
silver  chloride  forms  with  it  a  compound  which  is  soluble 
in  water;  and,  on  adding  an  acid,  the  ammonia  combines 
with  it,  leaving  the  silver  chloride  uncombined  and  there- 
fore insoluble. 

Extensive  use  is  made  of  insoluble  compounds  for  the 
purpose  of  detecting  substances  in  analysis.  The  principal 
insoluble  chlorides  are  those  of  silver,  lead,  and  mercury.* 

*  There  are  two  chlorides  of  mercury.    Only  one  of  them,  mercur- 
ous  chloride,  is  insoluble. 
19 


290  INTRODUCTION  TO  CHEMISTRY. 

If,  therefore,  on  adding  hydrochloric  acid  or  a  soluble  chlo- 
ride to  a  solution,  a  precipitate  is  formed,  the  conclusion  is 
justified  that  one  or  more  of  the  three  metals  —  silver,  lead, 
or  mercury  —  is  present.  By  taking  account  of  the  dif- 
ferences in  the  properties  of  these  chlorides  it  is  not  difficult 
to  decide  of  which  of  them  a  precipitate  consists. 

Oxides.  —  These  occur  very  generally  in  nature,  and  are 
among  the  most  common  ores  of  some  of  the  important 
metals.  The  oxides  of  iron,  tin,  manganese,  etc.,  are  all 
found  in  nature.  They  can  be  made  by  oxidizing  the 
metals,  by  heating  nitrates  and  carbonates,  and  by  heating 
hydroxides. 

EXAMPLES.  —  When  magnesium  is  burned  (see  Experiment 
14)  it  is  converted  into  magnesium  oxide: 

Mg  +  0  =  MgO. 

When  lead  nitrate  is  heated,  it  gives  off  oxygen  and  an 
oxide  of  nitrogen  and  leaves  behind  lead  oxide: 


Pb(N03)2  =  PbO  +  2N03  +  0. 

When  calcium   carbonate   is  heated  it  gives  off  carbon 
dioxide  and  leaves  behind  calcium  oxide,  CaO: 

CaC03  =  CaO  +  C02. 

Hydroxides.  —  The  hydroxides  are  formed  by  treating 
oxides  with  water,  and  by  decomposing  salts  by  adding 
soluble  hydroxides. 

EXAMPLES.  —  When  calcium  oxide  or  lime  is  treated  with 
water  it  is  converted  into  the  hydroxide,  CaOaH2,  or  slaked 
lime. 

EXPERIMENT  127.  —  To  some  pieces  of  freshly  slaked  lime 


HYDROXIDES.  291 

•add  enough  cold  water  to  cover  it.     The  action  which  takes 
place  is  represented  by  the  equation 

CaO  +  HaO  =  Ca03Ha. 

The  process  is  known  as  slaking.  [What  evidence  have 
you  that  heat  is  evolved  in  the  reaction,  and  that  the  sub- 
stance obtained  is  not  calcium  oxide  ?] 

Most  of  the  hydroxides  of  the  metals  are  insoluble  in  water. 
If  a  soluble  hydroxide  is  added  to  a  solution  containing  a 
metal  whose  hydroxide  is  insoluble,  the  latter  is  precipitated. 
Thus,  if  a  solution  of  sodium  hydroxide  be  added  to  a 
solution  of  a  magnesium  salt,  magnesium  hydroxide  is 
precipitated: 


MgS04+  2NaOH  =  Na,S04  +  MgO.H... 

EXPERIMENT  128.  —  To  a  small  quantity  of  a  dilute  solu- 
tion of  magnesium  sulphate  add  a  dilute  solution  of  caustic 
soda.  The  white  precipitate  is  magnesium  hydroxide. 
[Would  you  expect  this  precipitate  to  be  soluble  in  sulphuric 
acid  ?  in  hydrochloric  acid  ?  in  nitric  acid  ?]  The  answers 
follow  from  these  considerations  :  When  acids  act  upon 
hydroxides,  salts  are  formed;  magnesium  sulphate  is  soluble, 
as  is  seen  by  the  fact  that  we  started  with  a  solution  of  this 
salt;  the  only  insoluble  chlorides  are  those  of  silver,  lead, 
and  mercury;  all  nitrates  are  soluble. 

When  a  solution  of  an  iron  salt  is  treated  with  sodium 
hydroxide  a  precipitate  of  iron  hydroxide  is  formed: 

Fe013  +  SETaOH  =  Fe03H3  +  3NaCl. 

EXPERIMENT  129.—  To  a  dilute  solution  of  that  chloride 
of  iron  which  is  known  as  ferric  chloride  add  caustic  soda. 


292  INTRODUCTION  TO  CHEMISTRY. 

The  reddish  precipitate  which  is  formed  is  ferric  hydroxide* 
[From  the  general  statements  made  above,  would  you  expect 
this  precipitate  to  be  soluble  in  sulphuric  acid  ?  in  hydro- 
chloric acid  ?  in  nitric  acid  ?  Try  each.] 

Only  the  hydroxides  of  the  members  of  the  potassium 
family  and  of  the  calcium  family  are  soluble  in  water.  The 
hydroxides  of  sodium  and  potassium  are  caljed  alkalies^ 
The  solution  of  ammonia  in  water  acts  like  a  soluble 
hydroxide  and  probably  contains  ammonium  hydroxide, 
NH4OH,  formed  by  the  action  of  water  on  ammonia: 

NH3  +  H20  =  NH4OH. 

When  any  one  of  the  soluble  hydroxides  is  added  to  a 
salt  containing  any  metal. which  does  not  belong  to  the 
potassium  or  calcium  family  an  insoluble  compound  is 
thrown  down. 

[Test  this  statement  by  trying  such  salts  as  may  be  avail- 
able. Note  the  results  in  each  case.  Is  an  insoluble  com- 
pound formed  ?  What  is  its  general  appearance  ?] 

Decomposition  of  Salts  by  Acids  and  by  Bases.—  The  de- 
composition of  salts  by  the  addition  of  hydroxides  is  in 
some  respects  analogous  to  the  decomposition  of  salts  by  the 
addition  of  strong  acids. 

When  -an  acid  is  added  to  a  salt  there  are  three  cases 
which  may  present  themselves: 

1.  The  acid  from  which  the  salt  is  derived  may  be  vola- 
tile or  may  break  up,  yielding  a  volatile  product. 

In  this  case  decomposition  takes  place,  and  the  volatile 
acid  is  given  off.  This  is  illustrated  by  the  liberation  of 
hydrochloric  and  nitric  acids  from  chlorides  and  nitrates 
by  the  addition  of  sulphuric  acid,  and  of  carbon  dioxide 
from  carbonates  by  the  addition  of  other  acids. 


DECOMPOSITION  OP  SALTS. 

[Write  the  equations  representing  the  action 
place  when   sulphuric  acid  acts  upon  potassiuL 
calcium   chloride,  sodium  nitrate,  calcium  nitrai 
hydrochloric  acid  acts  upon  sodium  carbonate,  calciu. 
bonate.] 

2.  The  acid  from  which  the  salt  is  derived  may  be  in- 
soluble or  difficultly  soluble  in  water,  and  not  volatile. 

Ig  this  case,  if  the  salt  is  in  solution  decomposition  takes 
place,  and  the  insoluble  or  difficultly  soluble  acid  is  preci- 
pitated. This  is  illustrated  by  the  liberation  of  boric  acid 
from  borax  by  the  addition  of  sulphuric  acid;  and  by  the 
liberation  of  silicic  acid  by  the  addition  of  hydrochloric  or 
sulphuric  acid  to  a  soluble  silicate. 

•3.  The  acid  from  which  the  salt  is  derived  may  be 
soluble  and  not  volatile  under  the  existing  conditions. 

In  this  case,  if  the  substances  are  in  solution,  apparently 
no  change  takes  place.  Thus,  when  nitric  acid  is  added  to 
sodium  chloride  in  solution  no  striking  change  takes  place, 
no  gas  is  given  off,  no  precipitate  is  formed.  It  is  an  ex- 
tremely difficult  thing  to  determine  what  does  take  place 
under  these  circumstances.  A  study  of  such  cases  as  this 
is  of  great  importance  to  chemistry,  but  cannot  be  under- 
taken at  this  stage. 

Now,  to  return  to  the  action  of  hydroxides  upon  salts ; 
when  a  soluble  base  acts  upon  a  salt,  three  cases  may  pre- 
sent themselves: 

1.  The  base  from  which  the  salt  is  derived  may  be  volatile 
or  may  break  up,  yielding  a  volatile  product. 

In  this  case  decomposition  takes  place  and  the  volatile 
base  is  given  off.  This  is  not  a  common  case  except  among 
the  compounds  of  carbon.  The  one  illustration  which  we 
have  had  is  the  decomposition  of  ammonium  salts  by  cal- 
cium hydroxide  and  sodium  hydroxide. 


INTRODUCTION  TO  CHEMISTRY. 

[Write  the  equations  representing  the  action  in  both 
cases.  In  what  does  the  analogy  between  the  decomposi- 
tion of  ammonium  salts  by  bases  and  of  carbonates  by  acids 
consist  ?] 

2.  The  hydroxide  or  base  from  which  the  salt  is  derived 
may  be  insoluble  or  difficultly  soluble  in  water,  and  not 
volatile. 

In  this  case,  if  both  the  salt  and  the  base  are  in  solution, 
decomposition  takes  place,  and  the  insoluble  or  difficultly 
soluble  hydroxide  or  base  is  precipitated.  This  has  already 
been  illustrated. 

3.  The   base   from  which   the   salt  is   derived  may  be 
soluble  and  not  volatile. 

In  this  case  we  have  no  direct  evidence  of  change.  Thus, 
when  sodium  hydroxide  is  added  to  potassium  nitrate,  noth- 
ing is  seen  except  a  clear  solution.  To  determine  what 
takes  place  is  a  difficult  matter.* 

Sulphides. — Many  sulphides  are  found  in  nature.  They 
are  made  by  heating  metals  with,  sulphur;  by  treating  solu- 
tions of  salts  with  hydrogen  sulphide  or  soluble  sulphides. 

EXAMPLES. — Among  the  common  natural  sulphides  are 
iron  pyrites,  FeS2;  lead  sulphide,  or  galenite,  PbS;  copper 

*  Here  a  word  of  warning  to  students.  Do  not  forget  that  when- 
ever a  precipitate  is  formed  there  is  something  in  the  solution  which 
is  just  as  important  as  the  precipitate.  Accustom  j'ourselves  to  re- 
gard every  case  of  chemical  action  as  a  whole.  The  statement  that 
a  precipitate  is  formed  when  sodium  hydroxide  is  added  to  a  solution 
of  an  iron  salt  is  a  very  imperfect  description  of  the  chemical  change 
that  takes  place.  Precipitates  have  come  to  be  regarded  in  a  false 
light,  in  consequence  of  the  constant  use  made  of  them  for  purposes 
of  analysis.  It  must  be  remembered  that  analysis  is  not  chemistry, 
though  it  is  essential  to  the  study  of  chemistry  and  is  an  important 
application  of  the  science.  The  art  of  analysis  is  founded  upon  a 
knowledge  of  the  science  of  chemistry.  If  you  have  a  knowledge  of 
the  science,  it  will  be  easy  to  acquire  the  art  of  analysis,  should  this 
acquisition  become  desirable. 


SULPHIDES.  295 

pyrites,  FeCuS2.  [Examine  several  specimens  of  each,  and 
note  their  general  properties.] 

When  copper  or  iron  is  heated  with  sulphur  the  corre- 
sponding sulphides  are  formed.  (See  Experiments  10  and 
112.)  [For  what  purpose  were  these  experiments  per- 
formed ?] 

When  hydrogen  sulphide  is  passed  through  a  solution 
containing  a  metal  whose  sulphide  is  insoluble,  the  sul- 
phide is  precipitated.  This  has  been  illustrated  by  passing 
the  gas  through  solutions  of  lead  nitrate,  zinc  sulphate,  and 
arsenic  trioxide.  The  reactions  are  : 


+  H2S  =  PbS 
ZnS04  +  H2S  =  ZnS  +  H,SO4  ; 
As203  +  3H2S  =  As2S3  +  3H20. 

[What  differences  were  observed  in  these  three  cases? 
Repeat  the  experiments.] 

When  a  soluble  sulphide,  as  ammonium  sulphide  or  so- 
dium sulphide,  is  added  to  a  solution  containing  a  metal 
whose  sulphide  is  insoluble,  the  insoluble  sulphide  is 
thrown  down.  Add  ammonium  sulphide  successively  to 
dilute  solutions  of  an  iron  salt,  a  lead  salt,  a  copper  salt. 
Note  what  takes  place  in  each  case. 

The  sulphides  of  all  the  metals  except  those  which  be- 
long to  the  lithium  and  calcium  families,  and  that  of  mag- 
nesium, are  insoluble  in  water.  Of  those  sulphides  which 
are  insoluble  in  water,  some  are  insoluble  and  some  are 
soluble  in  dilute  hydrochloric  acid.  Further,  of  those 
which  are  insoluble  in  dilute  hydrochloric  acid,  some  are 
soluble  and  some  are  insoluble  in  ammonium  sulphide. 

These  facts  furnish  the  basis  of  the  method  most  common- 
ly made  use  of  in  analyzing  substances.  Suppose  we  have  a 


296  INTRODUCTION  TO  CHEMISTRY. 

solution  containing  all  the  more  common  elements,  and  we 
wish  to  determine  what  is  in  it.  [If,  on  adding  hydrochlo- 
ric acid,  a  precipitate  is  formed,  what  does  this  show?]  This 
precipitate  is  filtered  off,  and  treated  with  hydrogen  sul- 
phide. Those  metals  whose  sulphides  are  insoluble  in 
dilute  hydrochloric  acid  will  be  precipitated.  Among  the 
elements  which  may  be  contained  in  this  precipitate  are 
lead,  mercury,  copper,  tin,  arsenic.  The  solution  from 
which  the  precipitate  was  thrown  down  may  still  contain 
those  metals  whose  sulphides  are  soluble  in  dilute  hydro- 
chloric acid.  If,  therefore,  we  filter  off  the  precipitate  and 
add  ammonium  sulphide  to  the  filtrate,  the  metals  whose 
sulphides  are  insoluble  in  neutral  or  alkaline  solutions  will 
be  thrown  down.  Among  these  are  iron,  aluminium,  chro- 
mium, manganese,  etc.  The  filtrate  from  this  precipitate 
may  contain  all  those  metals  whose  sulphides  are  soluble  in 
water.  By  means  of  other  reactions  these  can  be  subdi- 
vided into  groups.  In  the  ordinary  method  of  analysis  we 
have,  therefore,  several  groups  of  elements  to  deal  with. 
These  are : 

1.  TJie  hydrochloric-acid   group,    consisting    of    those 
metals  whose  chlorides  are  insoluble  in  water. 

2.  The  hydrogen- sulphide  group,   consisting    of    those 
metals  whose  sulphides  are  insoluble  in  dilute  hydrochloric 
acid. 

3.  The  ammonium- sulphide  group,  consisting  of   those 
metals  whose  sulphides  are  soluble  in  dilute  hydrochloric 
acid,  but  are  precipitated  by  ammonium  sulphide. 

4.  Elements  whose  sulphides  are  soluble  in  water. 

Each  of  these  groups  can  be  subdivided,  and  the  sub- 
groups again  subdivided,  until  positive  evidence  of  the 
presence  of  certain  metals  is  obtained. 


NITRATES.  297 

Hydrosulphides  are  formed  when  hydrogen  sulphide  is 
passed  into  a  solution  of  a  hydroxide  until  no  more  is  taken 
up. 

Potassium  hydrosulphide  is  formed  thus': 

KOH  +  HaS  =  KSH  +  HaO. 
Ammonium  hydrosulphide  is  formed  thus  : 
NH4OH  +  H2S  =  NH4SH  +  H20. 

Nitrates. — These  salts  are  formed  by.  treating  metals 
with  nitric  acid;  by  treating  oxides  or  hydroxides  with 
nitric  acid,  and  in  general  by  treating  any  easily  decom- 
posed salt  as  a  carbonate  with  nitric  acid. 

EXAMPLES.— When  nitric  acid  acts  upon  copper,  copper 
nitrate  is  formed.  [What  else  is  formed?  Give  an  account 
of  the  changes  which  take  place.  Write  the  equation  rep- 
resenting the  reaction.]  . 

The  simple  neutralization  of  nitric  acid  with  a  base  or 
hydroxide  has  been  illustrated  in  the  experiments  on  acids 
and  bases  (Experiment  61).  [Write  the  equations  repre- 
senting the  reactions  which  take  place  when  nitric  acid  is 
neutralized  with  potassium  hydroxide,  with  calcium  oxide, 
with  calcium  hydroxide.] 

All  nitrates  are  soluble  in  water,  and  all  are  decomposed 
by  heat.  [Try  the  solubility,  in  water,  of  such  nitrates  as 
may  be  available.] 

EXPEEIMENT  130.— Heat  2  to  3  grams  potassium  nitrate 
on  charcoal  with  the  blow-pipe  flame.  The  decomposition 
with  evolution  of  gas  is  called  deflagration.  Heat  some 
copper  nitrate  and  lead  nitrate.  Carefully  note  the  changes 


298  INTRODUCTION  TO  CHEMISTRY. 

which  take  place.  The  compounds  left  behind  are  coppei 
oxide  and  lead  oxide. 

Chlorates  are  made  from  potassium  chlorate,  which  is 
made  by  treating  a  strong  solution  of  caustic  potash  with 
chlorine.  [Explain  the  reaction.] 

Chlorates  are  soluble  in  water,  and  are  decomposed  by 
heat  with  evolution  of  oxygen.  [When  potassium  chlorate 
is  heated,  what  takes  place  in  the  first  stage  of  the  oper- 
ation?]- 

Hypochlorites  are  formed  by  treating  some  of  the  metal- 
lic hydroxides  in  dilute  solution  with  chlorine.  This  has 
been  illustrated  in  the  formation  of  "  bleaching-powder," 
which  contains  calcium  hypochlorite.  [Explain  what  takes 
place  when  slaked  lime  is  treated  with  chlorine.] 

Hypochlorites  are  decomposed  by  heat. 

Sulphates. — Some  sulphates,  as  those  of  calcium  and  ba- 
rium, are  found  in  nature,  the  former  being  known  as  gyp- 
sum. Sulphates  are  made  by  treating  metals  or  metallic 
hydroxides  or  oxides  with  sulphuric  acid;  by  treating  easily 
decomposed  salts,  as  carbonates,  with  sulphuric  acid;  and  by 
treating  a  solution  containing  a  metal  whose  sulphate  is 
insoluble  with  sulphuric  acid  or  a  soluble  sulphate. 

EXAMPLES. — Usually,  when  sulphuric  acid  acts  upon  a 
metal,  hydrogen  is  evolved  and  a  salt  is  formed.  This 
has  been  illustrated  in  the  preparation  of  hydrogen  by 
means  of  zinc  and  sulphuric  acid. 

EXPERIMENT  131. — Dissolve  some  iron  in  dilute  sulphu- 
ric acid.  When  the  acid  is  neutralized,  filter  the  solution 
and  evaporate  if  down  to  crystallization.  [What  is  the  ap- 
pearance of  the  salt?  Does  it  contain  water  of  crystalli- 
zation? Was  hydrogen  evolved  during  the  action  of  the 


SULPHATES.  299 

acid  on  the  metal?]    Dry  some  of  the  salt,  and  put  it  aside 
for  further  use. 

EXPERIMENT  132. — Dissolve  some  copper  foil  in  concen- 
trated sulphuric  acid.  [In  what  respect  does  the  action  in 
this  case  differ  from  that  in  the  last  experiment?]  Evapo- 
rate the  solution,  and  get  out  some  of  the  salt  in  the  form 
of  crystals.  [What  is  the  appearance  of  the  salt?  Does  it 
contain  water  of  crystallization?  What  does  the  salt  look 
like  after  it  has  been  heated  in  a  tube?]  Dry  some  of  it, 
and  put  it  aside  for  further  use.  [Write  the  equations  rep- 
resenting the  action  which  takes  place  when  copper  acts 
upon  sulphuric  acid.] 

The  action  of  sulphuric  acid  on  metallic  hydroxides  has 
been  illustrated.  (See  Experiment  61.) 

[Write  the  equation  representing  the  action  which  takes 
place  when  the  acid  acts  upon  sodium  hydroxide,  potassium 
hydroxide,  ammonium  hydroxide.  What  is  monosodium 
sulphate?  What  is  neutral  sodium  sulphate?  Is  there  any 
difference  between  disodium  sulphate  and  neutral  sodium 
sulphate?] 

Most  sulphates  are  soluble  in  water.  The  sulphates  of 
barium,  strontium,  and  lead  are  insoluble  in  water,  and 
the  sulphate  of  calcium  is  difficultly  soluble.  Therefore, 
if  sulphuric  acid  be  added  to  a  solution  containing  either 
of  the  metals  barium,  strontium,  or  lead,  a  precipitate  will 
be  formed. 

EXPERIMENT  133. — Make  a  dilute  solution. gf  barium 
chloride,  of  lead  nitrate,  of  strontium  nitrate'.  To  a  small 
quantity  of  each  in  a  test-tube  add  a  little  sulphuric  acid. 
In  each  case  a  white  precipitate  is  formed.  [What  remains 
in  solution?]  Make  a  somewhat  concentrated  solution  of 
calcium  chloride.  To  this  add  some  sulphuric  acid.  A 


300  INTRODUCTION  TO  CHEMISTRY. 

precipitate  is  formed.  [What  is  in  solution?]  Add  more 
water,  and  see  whether  this  precipitate  will  dissolve.  The 
formulas  of  the  salts  used  in  the  experiments  are  barium 
chloride,  BaCl2;  lead  nitrate,  Pb(N03)2;  strontium  nitrate, 
Sr(N08)a.  [Write  the  equations  expressing  the  reactions.] 
If  to  the  solutions  of  the  salts  any  soluble  sulphate  be 
added  instead  of  sulphuric  acid,  the  same  insoluble  sul- 
phates will  be  formed.  The  sulphates  of  iron,  copper,  so- 
dium, and  potassium  are  among  the  soluble  sulphates. 
Make  dilute  solutions  of  small  quantities  of  each  of  these, 
and  add  them  successively  to  the  solutions  of  barium  chlo- 
ride, lead  nitrate,  and  strontium  nitrate.  The  formula 
of  iron  sulphate  is  FeS04;  of  copper  sulphate,  CuS04;  of 
sodium  sulphate,  Na2S04;  and  potassium  sulphate,  K2S04. 
Write  the  equations  representing  the  reactions  which  take 
place  in  the  above  experiments.  It  need  hardly  be  ex- 
plained that  the  action  consists  in  an  exchange  of  places  on 
the  part  of  the  metals.  Thus,  when  the  soluble  salt  iron 
sulphate,  FeS04,  is  brought  together  with  the  soluble  salt 
barium  chloride,  BaCl2,  the  insoluble  salt  barium  sulphate, 
BaS04,  and  the  soluble  salt  iron  chloride,  FeCl2,  are  formed: 

FeS04  +  Bad,  =  FeCl2  +  BaS04. 

As  a  rule,  sulphates  are  not  decomposed  by  heat. 

EXPERIMENT  134. — Heat  successively  specimens  of  the 
sulphates  of  sodium,  potassium,  iron,  and  copper  in  a  por- 
celain crucible  over  the  flame  of  a  Bunsen  burner  or  an 
alcohol  lamp.'  After  cooling,  see  whether  the  substances 
left  in  the  crucible  are  sulphates.  Dissolve  in  water  and 
add  to  a  solution  of  barium  chloride. 

When  heated  with  charcoal  in  the  reducing  flame  of  the 
blow-pipe,  sulphates  are  reduced  to  sulphides : 


CARBONATES.  301 

KaS04  +  40  =  KaS  +  400,  or 
KaS04  +  20  =  K2S  +  2C03. 

ExPEEIMENT  135. — Mix  and  moisten  a  little  sodium  sul- 
phate and  finely  powdered  charcoal.  Heat  the  mixture  for 
some  time  in  the  reducing  flame.  After  cooling  scrape  off 
the  salt,  dissolve  it  in  a  few  cubic  centimetres  of  water  and- 
filter  through  a  small  filter.  If  the  change  to  the  sulp'hide 
has  taken  place,  sodium  sulphide,  Na2S,  is  in  solution.  A 
soluble  sulphide  when  added  to  a  solution  containing  cop- 
per gives  a  black  precipitate  of  copper  sulphide.  Try 
this;  also  try  the  action  on  copper  of  some  of  the  sulphate 
from  which  the  sulphide  was  made. 

Sulphites  are  made  from  sodium  or  potassium  sulphite, 
which  are  made  by  treating  sodium  or  potassium  hydrox- 
ide in  solution  with  sulphur  dioxide  : 

OTaOH  +  S02  =  Na2S03  +  H20. 

All  sulphites  are  decomposed  by  the  common  acids,  sul- 
phur dioxide  being  given  off: 

Na2S03  +  H2S04  =  NaaS04  +  H20  +  S0a. 

Carbonates.  —  Many  carbonates  are  found  in  nature, 
some  of  them  in  great  abundance,  and  widely  distributed. 
The  principal  one  is  calcium  carbonate.  They  are  made 
by  passing  carbon  dioxide  into  solutions  of  hydroxides, 
and  by  adding  soluble  carbonates  to  solutions  of  salts  con- 
taining metals  whose  carbonates  are  insoluble. 

EXAMPLES. — The  formation  of  potassium  carbonate  by 
the  treatment  of  potassium  hydroxide  with  carbon  dioxide 
has  already  been  illustrated.  (See  Experiments  93  and  94.) 


302  INTRODUCTION  TO  CHEMISTRY. 

[Write  the  equation  representing  the  action.  Is  the  salt 
formed  in  this  case  soluble  or  insoluble  in  water  ?] 

The  formation  of  calcium  carbonate  by  passing  carbon 
dioxide  into  a  solution  of  calcium  hydroxide  (lime-water) 
has  been  illustrated  under  the  head  of  carbon  dioxide. 

[Describe  the  experiment.  Write  the  equation  repre- 
senting the  action  in  this  case.  Is  calcium  carbonate  sol- 
uble' or  insoluble  in  water  ?  In  hydrochloric  acid,  in  sul- 
phuric acid,  in  nitric  acid  ?  What  action  takes  place  with 
each  of  these  acids  ?] 

EXPEEIMENT  136.— The  formation  of  carbonates  by  the 
addition  of  soluble  carbonates  to  solutions  of  salts  of 
metals  whose  carbonates  are  insoluble  is  illustrated  by  the 
following  experiments  :  Make  solutions  of  copper  sulphate, 
iron  sulphate,  lead  nitrate,  silver  nitrate,  calcium  chloride, 
barium  chloride.  Add  to  each  a  little  of  a  solution  of  a  sol- 
uble carbonate,  as  sodium  carbonate,  potassium  carbonate, 
ammonium  carbonate.  Note  the  result  in  each  case.  Filter 
off  all  the  precipitates  and  prove  that  they  are  carbonates. 
This  may  be  done  by  treating  them  with  dilute  acids, 
which  decompose  them,  causing  an  evolution  of  carbon 
dioxide,  which  can  be  detected  by  passing  a  little  of  it  into 
lime-water.  Write  all  the  equations  representing  the  reac- 
tions which  take  place  in  the  above  experiments.  Here 
again,  as  in  the  experiments  with  the  sulphates,  the  metals 
exchange  places : 

CuS04  +  Na2CO*3  =  Na2S04  +  OuCO,. 

[Is  copper  bivalent  or  univalent  if  the  formula  of  copper 
sulphate  is  CuS04?] 

All  carbonates  except  those  of  the  members  of  the  potas- 
sium family  are  insoluble,  and  «re  decomposed  by  heat  into 


PHOSPHATES.  303 

carbon  dioxide  and  the  oxide  of  the  metal.  The  decompo- 
sition of  calcium  carbonate  into  lime  and  carbonate  is  the 
best-known  illustration  of  this  fact : 

CaC03  =  CaO  +  C0a. 

Phosphates. — Calcium  phosphate  is  very  abundant  in 
nature,  and  a  few  other  phosphates  are  also  found.  The 
methods  for  making  phosphates  are  in  principle  the  same 
as  those  used  for  making  sulphates. 

The  phosphates  of  all  the  metals  except  the  members  of 
the  potassium  family  are  insoluble  in  water.  The  normal 
phosphates  [what  is  a  normal  phosphate  ?],  as  a  rule,  are 
not  changed  by  heat.  Those  phosphates  in  which  two 
thirds  of  the  hydrogen  is  replaced  by  metal — as,  for  ex- 
ample, disodium  phosphate,  HNa2P04 — lose  water  when 
heated,  and  yield  pyrophosphates  : 

2HNa,PO,  =  Na4P207  +  HaO. 

Sodium 
pyrophosphate. 

Those  phosphates  in  which  only  one  third  of  the  hydro- 
gen is  replaced  by  metal — as,  for  example,  monosodium 
phosphate,  HaNaP04 — lose  water  when  heated,  and  yield 
metaphosphates : 

HaNaP04  =  NaP03  +  H30. 

Sodium 
metaphosphate. 

Neither  the  pyrophosphates  nor  metaphosphates  are 
changed  by  heat. 

Silicates. — The  extensive  occurrence  of  silicates  in  nature 
has  been  spoken  of.  Those  which  are  most  abundant  are 
the  feldspars  and  their  decomposition  products.  The  prin- 


304  INTRODUCTION  TO  CHEMISTRY. 

cipal  feldspar  is  a  complex  silicate  of  aluminium  and  potas- 
sium, of  the  formula  KAlSi308,  derived  from  the  polysilicic 
acid  H4Si308  [what  is  a  polysilicic  acid  ?]: 

3H2Si03  =  H4Si308  +  H20. 

Silicates  may  be  made  by  heating  together  at  a  high 
temperature  silicon  dioxide,  in  the  form  of  fine  sand,  and 
bases. 

EXPERIMENT  137. — Mix  together  some  fine  sand  and 
about  four  times  its  weight  of  a  mixture  of  potassium  and 
sodium  carbonates.  Heat  in  a  platinum  crucible  in  the 
flame-  of  the  blast-lamp  *  until  the  mass  is  thoroughly 
melted.  Pour  the  molten  mass  out  on  a  stone,  and  when 
cooled  break  it  up  and  treat  it  with  water.  What  passes 
into  solution  is  a  mixture  of  potassium  and  sodium 
silicates: 

NaaC03  +  Si03  =  Na2Si08  +  C09. 

Some  silicates  are  decomposed  by  the  ordinary  acids,  such 
as  sulphuri.c  and  nitric  acids,  the  silicic  acid  separating  as  a 
difficultly  soluble  substance,  which  loses  water  and  becomes 
insoluble. 

EXPEEIMENT  135.— Treat  a  little  of  the  solution  contain- 
ing sodium  and  potassium  silicates,  prepared  in  the  last 
experiment,  with  a  little  sulphuric  or  hydrochloric  acid. 
A  gelatinous  substance  will  be  precipitated.  This  is  silicic 
acid.  Some  of  the  acid  remains  in  solution: 

NaaSi03  +  H3S04  =  NaaS04  +  H2Si03. 
By  evaporating  the  solution  to  dryness  and  heating  for 
*  This  is  nothing  but  a  large  blow-pipe  worked  by  a  foot-bellows. 


SILICATES.  305 

a  time  on  the  water-bath,  all  the  silicic  acid  is  converted  into 
silicon  dioxide,  which  is  entirely  insoluble. 

Many  silicates  which  are  not  acted  upon  by  strong  acids 
are  decomposed  by  fusing  with  sodium  or  potassium  car- 
bonate. 

Silicates  which  are  not  decomposed  in  either  of  the  ways 
mentioned  yield  to  hydrofluoric  acid.  The  action  consists 
in  the  formation  of  the  gas,  silicon  tetrafluoride,  SiF4,  and 
the  fluorides  of  the  metals  present.  Thus,  the  reaction  in 
the  case  of  feldspar  takes  place  in  accordance  with  the 
equation 

KAlSi308  +  16HF  =  KF  +  A1F8  +  3SiF4  +  8HaO; 

The  silicon  fluoride  is  given  off  and  the  fluorides  of  the 
metals  are  soluble  in  water.  Hence  hydrofluoric  acid  dis- 
solves the  silicate.  [Is  this  use  of  the  word  dissolves  strictly 
correct  ?] 

Having  thus  briefly  considered  some  of  the  chief  methods 
of  preparation  and  the  principal  general  properties  of  the 
compounds  of  the  metals,  we  may  now  take  up  such  facts  in 
regard  to  the  individual  metals  and  their  derivatives  as 
are  of  special  interest.  It  must  be  borne  in  mind  that  a 
thorough  knowledge  of  the  chemistry  'of  these  substances 
can  only  be  acquired  by  a  long  course  of  laboratory  practice. 
20 


CHAPTEE  XVIII. 

THE  POTASSIUM    FAMILY:    LITHIUM,   SODIUM,   POTAS- 
SIUM,  CAESIUM,    RUBIDIUM  (AMMONIUM). 

THE  most  widely  distributed  and  hence  best-known  mem- 
bers of  this  family  are  sodium  and  potassium.  The  hy- 
pothetical metal  ammonium  is  included  in  the  famil} 
because  the  salts  formed  by  ammonia,  in  which  this  hy 
pothetical  metal  is  considered  to  be  present,  very  closel} 
resemble  the  salts  of  potassium  and  sodium.  The  member? 
of  the  family  are  generally  called  the  metals  of  the  alkalies, 
as  the  two  best-known  members  are  obtained  from  the 
alkalies,  caustic  potash  and  caustic  soda,  or  potassium  and 
sodium  hydroxides. 

Potassium,  K  (At.  Wt.  39). — This  element  is  a  con- 
stituent of  many  minerals,  particularly  of  feldspar,  which,  as 
already  explained,  is  a  complex  silicate  of  aluminium  and 
potassium.  The  natural  decomposition  of  minerals  con- 
taining potassium  gives  rise  to  the  presence  of  this  metal, 
in.  various  forms  of  combination  everywhere  in  the  soil.  It 
is  taken  up  by  plants;  and  when  vegetable  material  is 
burned  the  potassium  remains  behind,  chiefly  as  potassium 
carbonate.  When  wood-ash  is  treated  with  water  the 
potassium  carbonate  is  dissolved,  and  it  may  be  obtained  in 
an  impure  state  by  evaporating  the  solution.  The  sub- 
stance thus  obtained  is  called  potash. 

EXPERIMENT  139.— Treat  two  or  three  litres  of  wood- 
ashes  with  water.  Filter  off  the  solution,  and  examine  it 


POTASSIUM.  307 

by  means  of  red  litmus-paper.  The  color  of  the  paper  is 
changed  to  blue.  Plainly  the  solution  is  alkaline.  Ex- 
amine some  potassium  carbonate.  [Does  its  solution  act  in 
the  same  way  ?]  Evaporate  the  solution  to  dryness.  Col- 
lect the  dry  residue  and  treat  it  with  dilute  hydrochloric 
acid.  [Is  a  gas  given  off  ?  Is  it  carbon  dioxide  ?] 

Potassium  is  also  found  in  the  form  of  the  chloride  KC1, 
accompanying  the  chloride  of  sodium,  and  as  the  nitrate  in 
saltpetre. 

The  metal  was  first  prepared  by  the  action  of  a  powerful 
electric  current  on  potassium  hydroxide.  It  is  now 
manufactured  by  distilling  a  mixture  of  potassium  car- 
bonate and  charcoal : 

K2C03+2C  =  2K-f  SCO. 

It  is  a  light  substance,  which  floats  on  water.  [Have 
you  had  evidence  of  this  ?]  Its  freshly  cut  surface  has  a 
bright  metallic  lustre,  almost  white;  it  acts  upon  water 
with  great  energy,  causing  the  evolution  of  hydrogen,  which 
burns,  and  the  formation  of  potassium  hydroxide.  This 
reaction  has  already  been  considered  in  connection  with 
hydrogen.  [Turn  back  to  the  experiment  (Experiment" 27) 
and  perform  it  again.  It  will  now  appear  much  clearer.] 
In  consequence  of  its  action  on  water,  potassium  cannot  be 
kept  in  the  air.  It  is  kept  under  some  oil  upon  which  it 
does  not  act,  as  petroleum. 

Compounds  of  Potassium. — The  chief  compounds  of 
potassium  with  which  we  meet  are  the  iodide,  KI,  which  is 
extensively  used  in  medicine  and  in  photography;  the 
hydroxide,  or  caustic  potash,  KOH,  which  finds  extensive 
use  in  laboratories  ;  the  nitrate,  or  saltpetre,  KN03,  used 
in  the  manufacture  of  gunpowder ;  the  chlorate,  KC103, 


308  INTRODUCTION  TO  CHEMISTRY. 

used  in  the  preparation  of  oxygen  and  in  medicine ;  and 
the  carbonate,  K3C03. 

The  methods  used  in  preparing  some  of  these  compounds 
are  interesting,  as  illustrating  the  applications  of  the  prin- 
cip!es  of  chemistry. 

Potassium  iodide,  KI,  is  made  by  treating  caustic  potash 
with  iodine  until  the  solution  begins  to  show  a  permanent 
yellow  color,  which  is  an  indication/that  no  more  iodine 
will  be  taken  up.  The  action  is  tne  same  as  that  which 
takes  place  when  chlorine  acts  upon  warm  concentrated 
caustic  potash.  Both  the  iodide  and  iodate  are  formed  : 

6KOK  +  61  =  5KI  +  KI08  +  3H20. 

By  evaporating  off  all  the  water  and  heating  the  residue, 
the  iodate  is  decomposed  into  iodide  and  oxygen. 

EXPERIMENT  140. — Examine  a  bottle  of  crystallized 
potassium  iodide.  Taste  a  little.  Dissolve  some  in  water. 
Add  some  iodine  to  this  solution.  [Does  the  iodine  dis- 
solve?] Heat  a  little.  [Does  it  contain  water  of  crystalliza- 
tion?] Treat  a  crystal  or  two  with  a  few  drops  of  concen- 
trated sulphuric  acid.  [What  takes  place?  To  what  is  the 
appearance  of  violet  vapors  due?  How  many  gases  are 
given  off?  (See  Experiment  107.)] 

Potassium  Hydroxide,  KOH.—  This  well-known  sub- 
stance, commonly  called  caustic  potash,  is  prepared  by 
treating  potassium  carbonate  with  calcium  hydroxide  in  a 
silver  or  iron  vessel. 

EXPERIMENT  141. — Dissolve  50  grams  potassium  carbon- 
ate in  500  to  600  cc.  water.  Heat,  to  boiling  in  an  iron  or 
silver  vessel,  and  gradually  add  the  slaked  lime  obtained 
from  25  to  30  grams  of  good  quick-lime.  During  the  opera- 
tion the  mass  should  be  stirred  with  an  iron  spatula. 


POTASS1 UM  NITRA TE.  309 

After  the  solution  is  cool,  draw  it  off  by  means  of  a  siphon 
into  a  bottle.  This  may  be  used  in  experiments  in  which 
caustic  potash  is  required. 

The  reaction  is  based  upon  the  fact  that  calcium  carbon- 
ate is  insoluble,  and  that  potassium  carbonate  and  cakium 
hydroxide  are  soluble: 

K2C03  +  Ca02H3  =  CaCO,  +  2KOH. 

The  hydroxide  is  a  white  brittle  substance.  In  contact 
with  the  air  it  deliquesces  [what  does  this  mean?]  and  ab- 
sorbs carbon  dioxide.  It  is  a  very  strong  base.  [Explain  the 
action  which  takes  place  when  potassium  hydroxide  acts 
upon  ammonium  chloride,  NH4C1;  copper  sulphate,  OuS04; 
and  magnesium  nitrate,  Mg(N03)J. 

Potassium  Nitrate,  KN03.— This  salt  is  commonly  called 
saltpetre.  Its  occurrence  in  nature  has  already  been  spoken 
of  under  Nitric  Acid.  [What  are  the  conditions  which 
give  rise  to  its  formation?]  When  refuse  animal  matter  is 
left  to  undergo  decomposition  in  the  presence  of  bases, 
nitrates  are  always  the  end-products.  Advantage  is  taken 
of  this  fact  for  the  purpose  of  preparing  saltpetre  arti- 
ficially, the  process  being  carried  on  on  the  large  scale  in 
the  "saltpetre  plantations."  Most  of  the  saltpetre  which 
is  in  the  market  is  made  from  Chili  saltpetre,  or  sodium 
nitrate,  by  treating  it  with  potassium  chloride: 

NaN03+  KC1  =  KN03  +  NaOL 

Potassium  nitrate  crystallizes  in  long  rhombic  prisms  of 
salty  taste. 

It  is  used  in  the  preparation  of  sulphuric  acid  [what  role 
does  it  play  in  the  preparation  of  sulphuric  acid?],  and  of 
nitric  acid  [how  is  nitric  acid  obtained  from  it?].  Its  chief 


310  INTRODUCTION  TO  CHEMISTRY. 

use  is  in  the  manufacture  of  gunpowder.  The  value  of 
gunpowder  is  due  to  the  fact  that  it  explodes  readily, 
the  explosion  being  a  chemical  change  accompanied  by  a  sud- 
den evolution  of  gases.  When  the  powder  is  enclosed  in  a 
gun-barrel  the  gases  in  escaping  drive  the  ball  before 
them.  Gunpowder  is  made  of  a  mixture  of  saltpetre, 
charcoal,  and  sulphur.  When  heated  the  saltpetre  gives 
off  oxygen  and  nitrogen;  the  oxygen  combines  with  the 
charcoal,  forming  carbon  dioxide  and  carbon  monoxide,  and 
the  sulphur  combines  with  the  potassium,  forming  potas- 
sium sulphide.  When  a  mixture  of  saltpetre  and  charcoal 
is  burned,  the  reaction  which  takes  place  is  this  : 

2KN03  +  30  =  C02  +  CO  +  2N  +  K2C03. 

By  adding  the  necessary  quantity  of  sulphur  the  carbon 
dioxide,  which  would  otherwise  remain  in  combination  with 
the  'potassium  as  potassium  carbonate,  is  given  off  and 
potassium  sulphide  formed : 

2KN03  +  30  +  S  =  3C02  +  2N  +  K2S. 

EXPERIMENT  142. — Mix  together  15  grams  potassium 
nitrate  and  2.5  grams  powdered  charcoal.  Set  fire  to  the 
mass. 

[PROBLEM, — What  would  be  the  volume  at  760  mm.  and  0°  of 
the  gases  evolved  from  5  grams  of  gunpowder  containing  the 
constituents  in  exactly  the  proportions  given  above?] 

Potassium  Chlorate,  KC103. — This  salt  has  so  frequently 
been  referred  to  and  used  in  earlier  experiments  that  it -is 
not  necessary  to  say  anything  more  about  it  here. 

[Describe  the  method  of  preparation  and  decomposition 
by  heat.  What  takes  place  when  it  is  treated  with  sul- 
phuric acid?] 


SODIUM.  311 

*• 

Sodium,  Na  (At.  Wt.  23).—  Sodium  occurs  very  widely 
distributed  and  in  large  quantities,  principally  as  sodium 
chloride.  It  occurs  also  as  sodium  nitrate,  and  in  the  form 
of  silicate  in  many  minerals.  It  is  found  everywhere  in 
the  soil,  and  is  taken  up  by  plants,  especially  by  those 
which  grow  in  the  neighborhood  of  the  sea-shore  and  in 
the  sea. 

It  is  prepared  from  sodium  carbonate  by  the  same 
method  as  that  used  in  the  preparation  of  potassium,  the 
reaction  involved  being  represented  thus  : 


Na2C03  +  20  =  2Na  +  300. 

Its  properties  are  very  similar  to  those  of  potassium.  It 
is  light,  floating  on  water;  it  has  a  bright  metallic  lustre, 
and  is  soft.  It  decomposes  water,  but  not  as  actively  as 
potassium. 

[Describe  what  takes  place  when  a  small  piece  of  potas- 
sium is  thrown  upon  water  and  when  a  piece  of  sodium  is 
similarly  treated.  How  is  the  difference  accounted  for?] 

Sodium  has  a  strong  affinity  for  oxygen,  and  is  used  in 
some  chemical  processes  as  a  reducing  agent  [what  is  a  re- 
ducing agent?],  as,  for  example,  in  the  preparation  of 
silicon,  magnesium,  and  aluminium.  A  compound  of 
mercury  and  sodium,  known  as  sodium  amalgam,  is  used 
in  some  metallurgical  operations  connected  with  the  ex- 
traction of  silver  and  gold  from  their  ores. 

The  chief  compounds  of  sodium  are  the  chloride,  NaCl; 
the  hydroxide,  or  caustic  soda,  NaOH;  the  nitrate,  or  Chili 
saltpetre,  NaN03;  the  sulphate,  Na2S04;  the  carbonate, 
NaaC03;  and  the  lor  ate,  or  borax,  NaaB407. 

Sodium  Chloride,  Nad.  —  This  is  the  substance  which  is 
known  by  the  name  common  salt.  It  occurs  very  widely 


312  INTRODUCTION  TO  CHEMISTRY. 

distributed,  and,  as  it  is  easily  soluble,  much  of  the  water 
which  enters  into  the  ocean  contains  some  of  it  in  solution. 
Sea- water  contains  from  2J  to  3  per  cent.  In  some  places 
the  salt  is  taken  out  of  mines  in  solid  form ;  in  others, 
water  is  allowed  to  flow  into  the  mines,  and  to  remain  for 
some  time  in  contact  with  the  salt,  and  the  solution  thus 
formed  is  drawn  or  pumped  out  of  the  mine,  and  evapo- 
rated by  appropriate  methods. 

Sodium  chloride  crystallizes  in  colorless  and  transparent 
cubes.  Sometimes  that  which  occurs  in  nature  is  colored 
blue.  In  hot  water  it  is  but  little  more  soluble  than  in 
cold  water.  In  crystallizing,  the  crystals  enclose  water  not 
as  water  of  crystallization,  and  this  is  given  off  when  the 
crystals  are  heated,  the  action  being  accompanied  by  a 
crackling  sound. 

Salt  is  used  as  the  starting-point  in  the  preparation  of 
all  sodium  compounds  and  of  chlorine  and  hydrochloric 
acid. 

[How  are  chlorine  and  hydrochloric  acid  obtained  from 
it  ?  What  takes  place  when  a  solution  of  silver  nitrate 
is  added  to  a  solution  of  common  salt  ?  What  substances 
besides  silver  nitrate  act  in  the  same  way  ?] 

Sodium  Hydroxide,  NaOH. — This  is  commonly  called 
caustic  soda.  It  can  be  prepared  in  the  same  way  as  potas- 
sium hydroxide  ;  that  is,  by  treating  a  solution  of  sodium 
carbonate  with  lime.  [Explain  the  reaction.]  Its  proper- 
ties are  very  similar  to  those  of  caustic  potash  [Are  the 
hydroxides  of  the  metals  mostly  soluble  or  insoluble  sub- 
stances ?] 

Sodium  Nitrate,  NaN03. — This  is  the  salt  which  has  so 
frequently  been  referred  to  by  the  name  Chili  saltpetre. 
It  occurs  in  very  large  quantities,  and  is  the  chief  source  of 
nitric  acid.  It  is  cheaper  than  potassium  nitrate,  but  can- 


SODIUM  CARBONATE.  313 

not  be  substituted  for  it  in  the  manufacture  of  gunpowder, 
because  it  becomes  moist  in  the  air. 

Sodium  Sulphate,  Na2S04  -f  10H20.  —  The  common  name 
of  this  substance  is  Glauber's  salt.  It  is  manufactured  in 
enormous  quantities  for  the  purpose  of  converting  common 
salt  into  sodium  carbonate,  or  "soda": 


H2S04  =  Na,S04  +  2HC1. 


[What  becomes  of  the  hydrochloric  acid  which  is  given 
off?] 

The  salt  crystallizes  in  large  colorless  monoclinic  prisms, 
containing  10  molecules  of  water  of  crystallization,  Na2S04 
4-  10H20.  It  loses  water  when  left  in  contact  with  the 
air.  [Is  it  efflorescent  or  deliquescent  ?] 

Sodium  Carbonate,  Na2C03  +  10H20.—  This  salt,  com- 
monly called  soda,  is  one  of  the  most  important  of  manu- 
factured chemical  substances.  The  mere  mention  of  the 
fact  that  it  is  essential  to  the  manufacture  of  glass  and  soap 
will  serve  to  give  some  conception  of  its  importance.  It  is 
found  in  the  ashes  of  sea  plants,  just  as  potassium  carbon- 
ate is  found  in  the  ashes  of  those  plants  which  grow  on  the 
land.  We  are,  however,  not  dependent  on  sea  plants  for 
our  supply,  as  two  methods  have  been  devised  for  prepar- 
ing sodium  carbonate  from  sodium  chloride,  with  which 
nature  provides  us  in  such  abundance.  As  these  methods 
are  interesting  applications  of  chemical  principles,  it  will 
be  well  to  consider  them  briefly.  The  problem  to  be  solved 
is  to  convert  sodium  chloride,  NaCl,  into  sodium  carbon- 
ate, Na2C03.  The  process  devised  by  Le  Blanc  for  the 
French  government  during  the  ^Revolution,  when  the  sup- 
ply had  been  cut  off,  involves  four  reactions: 


314  INTRODUCTION  TO  CHEMISTRY. 

1st.  The  sodium  chloride  is  converted  into  sodium  sul- 
phate by  treating  it  with  sulphuric  acid: 

2Na01  +  H,S04  =  NaaS04  +  2HC1. 

3d.  The  sodium  sulphate  thus  obtained  is  heated  with 
charcoal,  which  reduces  it  to  sodium  sulphide,  NaaS: 

Na2S04  +  40  =  Na,S  +  4CO. 

3d.  The  sodium  sulphide  is  heated  with  calcium  carbon- 
ate, when  sodium  carbonate  and  calcium  sulphide  are 
formed: 

NaaS  +  CaC08  =  NaaC03  +  CaS. 

4th.  But  both  the  products  of  this  reaction  are  soluble 
in  water.  If  lime  is  present  it  forms,  however,  an  in- 
soluble compound  with  calcium  sulphide,  3CaS.CaO,  and 
this  can  easity  be  separated  from  the  sodium  carbonate. 

In  practice  the  sodium  sulphate  is  mixed  with  charcoal 
and  calcium  carbonate,  and  the  mixture  heated.  The  char- 
coal reduces  the  sulphate  to  the  sulphide,  which  acts  upon  the 
calcium  carbonate,  forming  sodium  carbonate  and  calcium 
sulphide.  But  some  of  the  calcium  carbonate  is  decom- 
posed by  the  heat  into  lime  and  carbon  dioxide: 

CaC03  =  CaO  +  C02 ; 

and  the  lime  thus  formed  combines  with  calcium  sulphide 
to  form  the  above-mentioned  insoluble  compound.  On 
treating  the  mass  with  water  after  cooling,  sodium  carbon- 
ate is  dissolved. 

Another  process  which  is  now  extensively  used  is  the  so- 
called  ammonia-soda  process.  This  depends  upon  the  fact 
that  monosodium  carbonate,  HNaC03,  is  comparatively 


AMMONIA-SODA  PROCESS.  315 

difficultly  soluble  in  water.  If,  therefore,  monoammonium 
carbonate,  or  acid  ammonium  carbonate,  HNH4C03,  is 
added  to  a  solution  of  common  salt,  acid  sodium  carbonate, 
HNaC03,  crystallizes  out,  and  ammonium  chloride  remains 
behind  in  the  solution: 

NaCl  +  HNH4C03  =  HNaC03  +  NH4C1. 

When  the  acid  carbonate  is  heated,  it  gives  off  carbon 
dioxide,  and  is  converted  into  the  normal  salt  thus: 

2HNaC03  =  Na2C03  +  C02  +  H20. 

The  carbon  dioxide  given  off  is  passed  into  ammonia, 
and  thus  again  obtained  in  the  form  of  acid  ammonium 
carbonate: 

NH3  +  H20  +  C02  =  HNH4C03. 

The  ammonium  chloride  obtained  in  the  first  reaction  is 
treated  with  lime  or  magnesia,  MgO,  and  the  ammonia  set 
free.  This  ammonia  is  again  used  in  the  preparation  of  acid 
ammonium  carbonate. 

EXPERIMENT  143. — Pass  carbon  dioxide  into  a  strong 
solution  of  ammonia  (about  100  cc.)  until  it  is  no  longer 
absorbed.  A  solution  of  acid  ammonium  carbonate  is 
thus  obtained.  Add  this  to  a  strong  solution  of  sodium 
chloride  as  long  as  a  precipitate  is  formed.  Filter  off  the 
precipitate,  and  dry  it  by  spreading  it  upon  layers  of  filter 
paper.  Heat  some  of  the  salt  when  dry,  and  determine 
whether  the  gas  given  off  is  carbon  dioxide  or  not.  When 
gas  is  no  longer  given  off  by  heat,  let  the  tube  cool  and 
.examine  the  residue.  [Is  it  a  carbonate  ?] 

Sodium  carbonate  crystallizes  in  large  monoclinio  prisms 


316  INTRODUCTION  TO  CHEMISTRY. 

with  10  molecules  of  water  of  crystallization.     The  crystals 
are  efflorescent. 

Disodium  Phosphate,  HNa3P04  -f  12H.,0.—  This  is  the 
common  form  of  sodium  phosphate.  It  is  formed  when 
phosphoric  acid  is  treated  with  sodium  carbonate  until  the 
solution  begins  to  show  an  alkaline  reaction  with  red  lit- 
mus. It  is  a  remarkable  fact  that,  although  phosphoric 
acid  is  tribasic,  and  with  most  metals  forms  salts  which  are 
derived  from  the  acid  by  replacement  of  all  the  three  hydro- 
gen atoms,  as  Ag3P04,  Ca3(P04)a,  etc.,  with  sodium  its  most 
stable  salt  is  the  one  in  which  two  hydrogen  atoms  are  re- 
placed by  sodium.  A  salt  of  the  formula  Na3P04  can  be 
made,  but  it  has  an  alkaline  reaction,  and  absorbs  carbon 
dioxide  from  the  air,  being  converted  into  sodium  carbon- 
ate and  disodium  phosphate: 


C03  +  H20  =  2HNa3P04  +  Na3C03. 


Sodium  Borate,  NaQB407  +  10H20.—  This  salt  has  been 
referred  to  under  boric  acid.  It  is  commonly  called  borax. 
It  is  found  in  nature  in  several  lakes  in  Asia,  and  in  this 
country  in  Clear  Lake,  Nevada.  It  is  manufactured  by 
neutralizing  the  boric  acid  found  in  Tuscany. 

When  heated,  borax  puffs  up,  and  at  red  heat  melts, 
forming  a  transparent  colorless  liquid.  This  is  anhydrous 
borax,  Na3B407.  Molten  borax  has  the  power  to  dissolve 
metallic  oxides,  and  forms  colored  glasses  with  some  of 
them.  It  is  used  in  blow-pipe  work  (see  Boric  Acid). 
Borax  is  an  antiseptic;  that  is  to  say,  it  prevents  the  de- 
composition of  organic  substances. 

Ammonium  Salts.  —  The  method  of  formation  of  the  so- 
called  ammonium  salts  has  been  described  (see  Ammonia). 


;\>-VA  u<u      0    M 

AMMONIUM  SULPHIDE.  317 

These  salts  resemble  the  salts  of  potassium  and  sodium  in 
many  respects,  and  they  are  hence  described  in  the  same 
connection.  The  chief  ones  are  the  chloride,  NH4C1;  the 
carbonate,  (NHJ.OO,;  the  sulphide,  (NH4)2S;  and  the 
hydrosulphide,  (NHJHS. 

Ammonium  Chloride,  NH4C1.— This  salt  is  commonly 
called  sal-ammoniac.  At  present  its  principal  source  is  the 
gas-works.  The  ammoniacal  liquor  of  the  works  is  neutral- 
ized with  hydrochloric  acid,  and  the  salt  obtained  by 
evaporation.  It  has  a  sharp,  salt  taste,  and  is  easily  soluble 
in  water.  When  heated  it  is  converted  into  vapor  without 
melting,  and  with  very  slight  decomposition ;  and  when 
the  vapor  comes  in  contact  with  a  cold  surface,  it  condenses 
in  the  form  of  crystals.  This  process  of  vaporizing  and 
condensing  a  solid  is  called  sublimation. 

EXPERIMENT  144. — On  a  piece  of  platinum  foil  or  por- 
celain heat  a  little  pure  ammonium  chloride.  It  will  pass 
off  and  form  a  dense  white  cloud.  This  is  the  same  cloud 
as  that  formed  by  bringing  together  gaseous  ammonia 
and  hydrochloric  acid.  All  ammonium  salts  are  either 
volatile  or  decompose  when  heated. 

[What  takes  place  when  ammonium  chloride  is  treated 
with  caustic  soda?  with  lime?  with  sulphuric  acid?] 

Ammonium  Sulphide,  (NH4)2S.  — This  substance  is  exten- 
sively used  in  chemical  analysis  for  the  purpose  of  precipi- 
tating those  sulphides  which  are  soluble  in  dilute  hydro- 
chloric acid.  As  will  be  remembered,  in  analyzing  a  mixt- 
ure of  substances  the  first  thing  usually  done  is  to  add 
hydrochloric  acid  to  the  solution.  This  precipitates  silver, 
lead,  and,  under  certain  conditions,  mercury.  This  pre- 
cipitate having  been  filtered  off,  hydrogen  sulphide  is  passed 
through  the  filtrate,  when  those  ineUls  whose  sulphides  are 


318  INTRODUCTION  TO  CHEMISTRY. 

insoluble  in  dilute  hydrochloric  acid  are  thrown  down. 
The  precipitate  is  filtered  off  and  ammonium  sulphide  added 
to  the  filtrate,  when  the  metals  whose  sulphides  are  soluble 
in  dilute  hydrochloric  acid  are  thrown  down.  Among 
these  are  iron,  cobalt,  nickel,  manganese,  etc.  Any  other 
soluble  sulphide  might  be  used,  but  the  advantage  of  am- 
monium sulphide  is  that  it  is  volatile,  and,  hence,  by  eva- 
porating the  solution  and  heating,  it  can  be  gotten  rid  of. 
Ammonium  sulphide  is  made  by  passing  hydrogen  sul- 
phide into  an  aqueous  solution  of  ammonia.  If  the  gas  is 
passed  until  the  solution  is  saturated,  the  product  is  the  hy- 
drosulphide  HNH4S: 

NH3  +  H2S  =  HNH4S. 

If  only  half  this  quantity  of  the  gas  is  passed,  the  product 
is  the  sulphide: 

2NH3  +  H2S  =  (NH4)2S. 

The  simplest  way  to  make  it  is  to  divide  a  quantity  of 
ammonia  solution  into  two  equal  parts.  Saturate  one  half, 
thus  forming  the  hydrosulphide,  and  add  the  other  half, 
when  this  reaction  takes  place: 


HNH4S  +  NH3  =  (NH4)2S. 

The  product  is  a  colorless  liquid  of  a  disagreeable  odor. 
It  soon  changes  color,  becoming  yellow,  and  after  a  time  a 
yellow  deposit  is  formed  in  the  vessel  in  which  it  is  con- 
tained. This  change  of  color  is  due  to  the  action  of  the 
oxygen  of  the  air.  Some  of  the  sulphide  is  decomposed 
into  ammonia,  water,  'and  sulphur: 

(NH4)2S  +  0  =  2NH,  +  H20  +  S. 


METALS  OF  THE  ALKALIES.  319 

The  sulphur  thus  set  free  combines  with  the  unde- 
composed  ammonium  sulphide,  forming  the  compounds 
(NH4)282,  (NH4)2S3,  etc.,  known  as  poly  sulphides.  When 
as  much  sulphur  as  possible  has  been  taken  up  in  this  way, 
any  more  which  may  be  set  free  by  the  action  of  oxygen  is 
deposited. 

A  solution  containing  the  polysulphides  is  called  yelloiv 
ammonium  sulphide.  It  is  used  to  dissolve  the  sulphides 
of  arsenic,  antimony,  and  tin  in  analytical  operations.  (See 
description  of  method  of  analysis,  p.  296.) 

EXPERIMENT  145. — Saturate  100  cc.  strong  aqueous  am- 
monia with  hydrogen  sulphide.  Add  to  the  saturated  so- 
lution 100  cc.  of  the  same  ammonia. 

Ammonium  Hydrosulphide,  HNH4S. — As  stated  above,  a 
solution  of  this  substance  is  made  by  passing  hydrogen  sul- 
phide into  a  solution  of  ammonia  until  no  more  is  taken  up. 

General  Characteristics  of  the  Metals  of  the  Alkalies. — 
From  what  has  been  said,  it  will  be  seen  that  nearly  all  the 
compounds  of  these  metals  are  soluble  in  water.  Of  those 
mentioned  only  monosodium  carbonate  is  at  all  difficultly 
soluble.  There  are  a  few  insoluble  salts  of  potassium, 
those  which  are  chiefly  used  in  analytical  operations  being 
the  chloro-platinate,  K2PtCl6,  which  is  formed  by  adding  a 
solution  of  platinum  chloride,  PtCl4,  to  a  solution  contain- 
ing potassium  chloride: 

2KC1  +  Pt014  =  K2PtCl6; 

and  ihe  fluo-silicate,  K3SiF6,  which  is  formed  when  a  solu- 
tion of  hydrofluo-silicic  acid,  H2SiF6,  is  added  to  a  solution 
containing  potassium. 

EXPERIMENT  146. — Add  platinum  chloride  and  hydro- 


320  INTRODUCTION  TO  CHEMISTRY. 

fluo-silicic  acid  successively  to  solutions  containing  potas- 
sium chloride. 

The  elements  lithium,  ccesium,  and  rubidium  are  much 
rarer  than  sodium  and  potassium.  While  for  the  chemist 
their  study  is  of  importance,  for  the  beginner  it  is  not  nec- 
essary. Lithium  is  found  in  a  form  of  mica  known  as 
lepidolite.  It  is  the  lightest  metal  known,  and  has  the 
smallest  atomic  weight,  viz.,  7.  The  relations  between  the 
atomic  weights  of  the  members  of  this  family  are  similar  to 
those  already  noticed  between  chlorine,  bromine,  and 
iodine;  sulphur,  selenium,  and  tellurium;  and  phosphorus, 
arsenic,  and  antimony.  Thus,  we  have  lithium,  7;  sodium, 
23;  and  potassium,  39.  The  atomic  weight  of  sodium,  23, 
is  the  mean  of  those  of  lithium,  7,  and  potassium,  39. 


Similarly,  the  atomic  weight  of  rubidium,  85,  is  nearly 
the.  mean  of*those  of  potassium  and  caesium,  133: 

39  -f-  133 


Flame  Reactions  and  the  Spectroscope.—  When  a  clean 
piece  of  platinum  wire  is  held  for  some  time  in  the  flame 
of  the  Bunsen  burner,  it  then  imparts  no  color  to  the  flame. 
"If  now  a  small  piece  of  sodium  carbonate  or  any  other  salt 
of  sodium  be  put  on  it,  the  flame  is  colored  intensely  yel- 
low. All  sodium  compounds  have  this  power,  and  hence 
the  chemist  makes  use  of  the  fact  for  the  purpose  of  de- 
tecting the  presence  of  sodium.  Similarly,  potassium  com- 
pounds color  the  flame  violet;  lithium  compounds  color  the 
flame  red;  and  the  other  metals  of  the  family  also  impart 
characteristic  colors  to  the  flame. 


FLA  ME  RE  A  CTIONS.  32 1 

EXPERIMENT  147. — Prepare  some  pieces  of  platinum 
wire,  8  to  10  c.m.  long,  with  a  loop  on  the  end  like  those 
described  for  blow-pipe  work.  After  thoroughly  cleaning 
them,  insert  one  in  a  little  sodium  carbonate,  and  notice  the 
color  it  gives  to  the  flame.  Try  another  with  potassium 
carbonate,  and,  if  the  substances  are  available,  others  with 
a  lithium  compound,  a  caesium,  and  a  rubidium  compound. 

While  it  is  an  easy  matter  to  recognize  potassium  alone, 
or  any  one  of  the  other  metals  alone,  it  is  difficult  to  do  so 
when  they  are  together  in  the  same  compound.  For  exam- 
ple, when  potassium  and  sodium  are  together,  the  intense 
yellow  caused  by  the  sodium  completely  masks  the  more 
delicate  violet  caused  by  the  potassium,  so  that  the  latter 
cannot  be  seen  with  the  unaided  eye.  In  this  particular 
case  we  can  get  over  the  difficulty  by  letting  the  light  pass 
through  a  blue  .glass,  or  a  thin  glass  vessel  filled  with  a  so- 
lution of  indigo.  The  yellow  light  is  thus  cut  off  while  the 
violet  light  passes  through  and  can  be  recognized.  A  more 
general  method  for  detecting  the  constituents  of  light  is  by 
means  of  a  prism.  Lights  of  different  colors  are  turned  out 
of  their  course  to  different  extents  when  passed  through  a 
prism,  as  is  seen  .when  white  sunlight  is  passed  through  a 
prism.  A  narrow  beam  of  white  light  passing  in  emerges 
as  a  band  of  various  colors,  called  its  spectrum.  We  thus 
see  that  white  light  is  made  of  different  colored  lights. 
Similarly,  we  can  determine  what  any  light  is  composed  of. 
Every  light  has  its  own  characteristic  spectrum.  The  light 
produced  by  burning  sodium,  or  by  introducing  a  sodium 
compound  in  a  colorless  flame,  has  a  spectrum  consisting  of 
a  narrow  yellow  band.  The  spectrum  of  potassium  consists 
essentially  of  two  bands,  one  red  and  one  violet.  Further, 
these  bands  always  occupy  4efinite  positions  relatively  to 


322  INTRODUCTION  TO  CHEMISTRY. 

one  another,  so  that,  on  looking  through  a  prism  at  the 
light  caused  by  potassium  and  sodium,  the  yellow  band  of 
sodium  is  seen  in  its  position,  and  the  two  potassium  bands 
in  their  proper  positions. 

The  instrument  used  for  the  purpose  of  observing  the 
spectra  of  different  lights  is  called  the  spectroscope.  It 
consists  essentially  of  a  prism  and  two  tubes.  Through 
one  of  the  tubes  the  light  to  be  examined  is  allowed  to 
pass  so  as  to  strike  the  prism  properly.  The  light  emerges 
from  the  other  side  of  the  prism,  and  is  observed  through 
the  other  tube,  which  is  provided  with  lenses  for  the  pur- 
pose of  magnifying  the  spectrum.  By  means  of  the  spec- 
troscope it  is  possible  to  detect  the  minutest  quantities  of 
some  elements,  and,  since  it  was  devised,  several  new  ele- 
ments have  been  discovered  through  its  aid,  as,  for  example, 
caesium,  rubidium,  thallium,  indium,  gallium,  and  others.* 


*  For  an  account  of  the  spectroscope  and  its  uses  the  student  is 
advised  to  consult  some  work  on  physics.     The  principles  involved 


in  its  construction  are  physical  principles,  and  cannot  properly  be 
text-book  of  chemistry. 


studied  in  full  in  a 


CHAPTER  XIX. 

THE    CALCIUM    FAMILY:    CALCIUM,    BARIUM, 
TIUM,   GLUCINUM. 

THE  three  elements  calcium,  barium,  and  strontium  re- 
semble one  another  very  closely.  Calcium  is  much  more 
abundant  than  either  of  the  other  members  of  the  family, 
while  strontium  is  the  least  abundant  of  the  three.  For 
the  present  it  will  be  best  to  confine  our  attention  to  the 
principal  member  of  the  family,  viz.,  calcium. 

Calcium,  Ca  (At.  Wt.  40).— This  element  occurs  very 
widely  distributed  in  nature,  and  in  enormous  quantities. 
It  is  found  principally  as  carbonate,  CaC03,  in  the  form  of 
limestone,  marble,  and  chalk;  as  sulphate,  CaS04,  in  the 
form  of  gypsum;  as  phosphate,  Ca3(P04)2,  in  phosphorite 
and  apatite;  as  fluoride,  CaF2,  in  fluor-spar. 

The  element  is  made  by  decomposing  calcium  chloride 
by  means  of  the  electric  current. 

It  is  a  brass-yellow  lustrous  substance,  which  in  moist  air 
becomes  covered  with  a  layer  of  hydroxide.  At  ordinary 
temperatures  it  decomposes  water  just  as  sodium  and  po- 
tassium do. 

The  principal  compounds  of  calcium  with  which  we  have 
to  deal  are  the  chloride,  CaCl2;  the  oxide,  or  quick-lime, 
CaO;  the  hydroxide,  or  slaked  lime,  Ca02H2;  ihehypochlo- 
n7e,Ca(OCl)2;  the  carbonate,  CaC03;  the  sulphate,  CaS04; 
the  phosphate,  Ca3(P04)2;  the  silicate,  in  the  form  of  glass. 


324  INTRODUCTION  TO  CHEMISTRY. 

Calcium  Chloride,  CaCla. — The  property  which  gives  this 
salt  its  value  is  its  power  to  absorb  water.  It  is  used  as  a 
drying  agent.  Gases  are  passed  through  it  for  the  purpose 
of  drying  them,  and  it  is  also  placed  in  vessels  in  which  it  is 
necessary  that  the  atmosphere  should  be  dry. 

•  EXPERIMENT  148.— Dissolve  10  to  20  grams  of  limestone 
or  marble  in  ordinary  hydrochloric  acid.  Evaporate  to 
dryness.  Expose  a  few  pieces  of  the  residue  to  the  air. 
[Does  it  become  moist  ?  In  what  experiments  has  calcium 
chloride  been  used,  and  for  what  purposes  ?  What  would 
happen  if  sulphuric  acid  were  added  to  calcium  chloride  ?] 
Try  it.  Explain  what  takes  place.  [Is  the  residue  soluble 
or  insoluble  in  water  ?] 

Calcium  Oxide,  CaO. — This  is  the  substance  commonly 
called  lime.  It  is  made  by  heating  calcium  carbonate, 
which  is  decomposed  into  lime  and  carbon  dioxide: 

CaC03  =  CaO  +  C03. 

[In  what  connection  have  we  already  met  with  this  re- 
action ?] 

Limekilns  are  large  furnaces  in  which  limestone  and 
other  forms  of  calcium  carbonate  are  heated  and  converted 
into  lime. 

[Why  is  it  dangerous  to  remain  for  any  length  of  time 
in  the  immediate  neighborhood  of  a  limekiln?] 

Lime  is  a  white,  amorphous,  infusible  substance.  When 
heated  in  the  flame  of  the  compound  blow-pipe,  it  gives 
forth  an  intense  light,  as  any  other  infusible  substance  would 
under  the  same  circumstances.  When  exposed  to  the  air, 
it  attracts  moisture  and  carbon  dioxide,  and  is  thus  con- 
verted into  the  carbonate.  It  must  hence  be  protected  from 
the  air. 


L1MSJ.  325 

Calcium  Hydroxide,  Ca02H2.—  When  calcium  oxide  or 
quick-liine  is  treated  with  water  it  becomes  hot  and  crum- 
bles to  a  fine  powder.  The  substance  which  is  formed  in 
this  operation  is  somewhat  soluble  in  water,  the  solution 
being  known  as  lime-water.  The  chemical  change  which 
takes  place  when  lime  is  treated  with  water  has  been  ex- 
plained. It  consists  in  the  formation  of  a  compound  of  the 
formula  CaO.,H2,  and  known  as  slaked  lime,  and  the  opera- 
tion is  known  as  slaking.  It  is  believed  that  just  as  potas- 
sium hydroxide,  KOH,  is  properly  regarded  as  water  in  the 
molecule  of  which  one  atom  of  hydrogen  is  replaced  by  an 
atom  of  potassium,  so  calcium  hydroxide  is  properly 
regarded  as  derived  from  water  by  the  replacement  of  two 
atoms  of  hydrogen  in  two  molecules  by  one  atom  of  the 
bivalent  metal  calcium: 

HOH  ~    ( OH 

HOH,  Ca|OHorCa(OH)a, 

Two  raol.  water.  Calcium  hydroxide. 

It  is  difficult  to  explain  to  the  beginner  exactly  why  this 
view  is  held.  It  can  only  be  said  that  it  is  a  conception 
which  is  in  harmony  with  a  great  many  facts,  though  it  does 
not  follow  as  a  necessary  consequence  from  any  facts  known 
to  us. 

EXPERIMENT  149.— To  40  to  50  grams  good  quick-lime 
add  100  cc.  water.  Soon  the  mass  will  begin  to  crumble, 
and  steam  will  rise  from  it,  indicating  that  heat  is  evolved. 
Afterwards  dilute  to  2  to  3  litres  and  put  the  whole  in  a  well- 
stoppered  bottle.  The  undissolved  lime  will  settle  to  the 
bottom,  and  in  the  course  of  some  hours  the  solution  above 
will  become  clear.  Carefully  pour  off  some  of  the  clear 
solution.  [What  takes  place  when  some  of  the  solution  is 
exposed  to  the  air  ?  When  the  gases  from  the  lungs  are 


826  INTRODUCTION  TO  CHEMISTRY. 

passed  through  it  ?  When  carbon  dioxide  is  passed  through 
it  ?  What  takes  place  when  dilute  sulphuric  acid  is  added 
to  lime-water  ?  Is  calcium  sulphate  difficultly  or  easily 
soluble  in  water  ?  Has  lime-water  an  alkaline  reaction  ?  ] 

When  potassium  hydroxide  is  added  to  a  solution  of  a 
salt  containing  a  metal  whose  hydroxide  is  insoluble  in 
water,  the  insoluble  hydroxide  is  precipitated.  This  was 
illustrated  in  Experiments  128  and  129.  [What  are  those 
experiments  ?]  Calcium  hydroxide  is  a  soluble  hydroxide, 
and  acts  in  the  same  way  that  potassium  hydroxide  does. 

EXPERIMENT  150. — Add  some  lime-water  to  a  solution 
of  ferric  chloride,  of  copper  nitrate,  of  lead  nitrate.  Ex- 
plain the  results. 

Calcium  hypochlorite,  Ca(OCl)2,  has  already  been  consid- 
ered to  a  sufficient  extent  under  the  head  of  Chlorine.  It 
need  only  be  repeated  that  the  form  in  which  chlorine  is 
transported  is  "bleaching-powder,"  which  is  a  compound 
containing  calcium  hypochlorite  and  calcium  chloride, 
Ca(OCl)2  -f  CaCl2,  made  by  .treating  slaked  lime  with 
chlorine  : 

2Ca(OH)2  +  401  =  Ca(OCl)2  +  CaCl2  +  2HaO. 
Bleaching-powder. 

Calcium  Carbonate,  CaC08.— This  salt  occurs  in  nature 
in  the  well-known  forms  calc-spar,  limestone,  marble,  and 
chalk.  The  variety  of  calc-spar  found  in  Iceland,  and 
known  as  Iceland  spar,  is  particularly  pure  calcium  ^r- 
bonate. 

It  crystallizes  usually  in  rhombohedrons,  as  seen  in  calc- 
spar.  It  is  insoluble  in  water,  and  is  decomposed  by  acids 
with  evolution  of  carbon  dioxide.  The  fact  that  it  is  solu- 


CALCIUM  SULPHATE.  327 

ble  in  water  containing  carbon  dioxide  in  solution,  and  that 
when  such  solutions  are  boiled  it  is  precipitated,  has  been 
commented  upon.  (See  Experiment  95.) 

Calcium  Sulphate,  CaS04  -f  2H20.—  Gypsum,  the  prin- 
cipal natural  variety  of  calcium  sulphate,  crystallizes  with 
two  molecules  of  water  of  crystallization,  CaS04  +  2H,0. 
When  heated,  it  loses  its  water  of  crystallization  and  forms 
a  powder  known  as  plaster  of  Paris,  which  has  the  power 
of  taking  up  water  and  forming  a  solid  substance.  The 
process  of  solidification  is  known  as  "  setting."  Plaster  of 
Paris  is  largely  used  in  making  casts. 

Calcium  sulphate  is  somewhat  soluble  in  water.  A  nat- 
ural water  containing  either  calcium  carbonate  or  sulphate 
in  solution  is  called  a  hard  water. 

It  is  a  curious  fact  that  when  anhydrous  gypsum,  or 
plaster  of  Paris,  has  taken  up  water  to  form  the  compound 
CaSO,,  -f-  2H20,  the  compound  differs  from  gypsum  very 
markedly  in  one  respect.  If  it  be  heated,  it  again  loses 
water;  but  the  anhydrous  powder  now  left  has  not  the 
power  to  take  up  water  again. 

EXPERIMENT  151. — Heat  some  powdered  gypsum  to 
about  200°  in  an  air-bath.  Examine  the  residue  and  see 
whether  it  will  become  solid  when  mixed  with  a  little  water 
so  as  to  form  a  paste. 

When  gypsum  is  treated  with  a  solution  of  the  carbonate 
of  an  alkali  metal,  as  sodium  carbonate  or  ammonium  car- 
bonate, it  is  completely  transformed  into  the  carbonate: 

(NH4)2C03  +  CaS04  -  (NH4)aS04  +  CaC08. 

EXPERIMENT  152.— Upon  a  gram  or  two  of  powdered 
gypsum  pour,  say,  100  cc.  of  a  moderately  strong  solution 


328  INTRODUCTION  TO  CHEMISTRY. 

of  ammonium  carbonate.  After  a  few  hours  pour  off  the 
solution,  collect  the  powder  on  a  filter,  and  see  whether  it 
has  changed  to  the  carbonate.  [How  can  you  determine 
whether  ammonium  sulphate  is  in  solution  or  not  ?]  Of 
course,  there  is  still  ammonium  carbonate  present,  and  this 
must  be  taken  into  account  in  examining  for  the  sulphate. 
We  usually  examine  for  a  sulphate  by  adding  a  soluble 
barium  salt,  when,  if  a  soluble  sulphate  is  present,  barium 
sulphate  is  precipitated.  In  this  case,  however,  the  am- 
monium carbonate  would  throw  down  barium  carbonate. 
To  prevent  this,  the  ammonium  carbonate  may  first  be  de- 
composed by  slowly  adding  sufficient  dilute  hydrochloric 
acid.  There  will  then  be  present  ammonium  chloride  and 
sulphate;  and,  now,  if  barium  chloride  or  any  other  soluble 
barium  salt  be  added,  barium  sulphate  will  be  precipitated. 

Calcium  Phosphate,  Ca3(P04)2.  —  The  normal  phosphate 
in  which  all  the  hydrogen  of  the  acid  is  replaced  by  cal- 
cium is  found  in  nature  as  phosphorite,  and  in  combination 
with  calcium  fluoride  or  chloride  as  apatite.  It  is  further 
the  chief  inorganic  constituent  of  bones,  and  is  found  in 
large  quantity  in  bone-ash.  It  is  found  everywhere  in  the 
soil  and  is  taken  up  by  plants.  It  is  formed  when  a  soluble 
phosphate  is  added  to  a  solution  of  a  calcium  salt. 

EXPERIMENT  153.  —  To  a  solution  of  calcium  chloride  in 
a  test-tube  add  disodium  phosphate,  HNa2P04.  The  pre- 
cipitate is  calcium  phosphate.  This  salt  is  decomposed  by 
hydrochloric  and  nitric  acids,  and  hence  dissolves  on  addi- 
tion of  these  acids  : 


2HNa,P04  +  30aCl2  =  Oa,(P04),  +  4NaCl  +  2HC1. 

I 
Monocalcium    Phosphate,    Ca(HaP04)a  +  fiaO.—  This  is 


MORTAR  AND  GLASS.  329 

commonly  called  the  acid  phosphate.  It  is  formed  when 
ordinary,  insoluble  calcium  phosphate  is  treated  with  con- 
centrated sulphuric  acid,  and  is  contained  in  the  so-called 
"  superphosphates. " 

Mortar. — Mortar  is  made  of  slaked  lime  and  sand.  When 
this  mixture  is  exposed  to  the  air,  carbonate  of  calcium  is 
slowly  formed  and  the  mass  becomes  extremely  hard.  The 
water  contained  in  the  mortar  soon  passes  off,  but  never- 
theless freshly  plastered  rooms  remain  moist  for  a  consider- 
able time.  This  is  due  to  the  fact  that  a  reaction  is  con- 
stantly taking  place  between  the  carbon  dioxide  and  calcium 
hydroxide  in  which  calcium  carbonate  and  water  are 
formed : 

Ca02H2  +  CO,  =  CaC03  +  H20, 

and  it  is  the  water  thus  liberated  which  keeps  the  air  moist. 
The  complete  conversion  of  the  lime  into  carbonate  re- 
quires a  very  long  time,  because  the  carbonate  which  is 
formed  on  the  surface  tends  to  protect  the  lime  in  the 
interior. 

Glass.— Common  glass  is  a  silicate  of  calcium  and  sodium, 
made  by  melting  together  sand  (silicon  dioxide,  Si02)  with 
lime,  or  calcium  carbonate,  and  sodium  carbonate.  When 
potassium  carbonate  is  used  instead  of  sodium  carbonate, 
the  glass  is  more  difficultly  fusible.  Bohemian  glass,  which 
is  so  extensively  used  in  the  manufacture  of  chemical  ap- 
paratus, is  a  silicate  of  calcium  and  potassium.  Flint-glass, 
which  has  a  high  refractive  power,  and  is  hence  especially 
valuable  for  the  manufacture  of  optical  instruments,  con- 
tains lead  instead  of  calcium.  It  is  much  more  easily 
fusible  than  calcium  glass. 

Colors  are  given  to  glass  by  putting  in  the  fused  mass 


330  INTRODUCTION  TO  CHEMISTRY. 

small  quantities  of  various  substances.  Thus  a  cobalt 
compound  makes  glass  blue  ;  copper  and  chromium  make 
it  green  ;  one  of  the  oxides  of  copper  makes  it  red.,  etc. 

The  compounds  of  barium  and  strontium  closely  resem- 
ble those  of  calcium.  Barium  forms  an  oxide,  BaO,  cor- 
responding to  lime,  and  also  another  one  known  as  barium 
dioxide,  Ba03.*  This  is  formed  by  passing  oxygen  or  air 
over  barium  oxide  heated  to  a  dull  red  heat.  At  a  higher 
temperature  it  gives  off  the  oxygen.  These  facts  have  re- 
cently been  utilized  for  the  purpose  of  extracting  oxygen 
from  the  air. 

Barium  oxide  is  converted  into  the  hydroxide  Ba02Ha 
when  treated  with  water.  This  hydroxide  is  soluble  in 
water,  the  solution  being  what  is  called  baryta-water. 

Calcium  compounds  color  the  flame  reddish  yellow  ; 
strontium  compounds,  intense  red ;  and  barium  com- 
pounds, yellowish  green. 

Between  the  atomic  weights  of  calcium,  strontium  and 
barium  there  exists  the  same  relation  as  that  with  which 
we  are  already  familiar  in  other  families.  The  atomic 
weight  of  calcium  is  40;  of  strontium,  87.5;  and  of  barium, 
137: 

*±  2??  =  88.5. 


*  This  compound  has  already  been  referred  to  in  describing  the 
preparation  of  hydrogen  dioxide,  H2Oa.  When  it  is  treated  with 
sulphuric  acid  this  reaction  takes  place: 

BaO2  -f  H2SO4  =  BaSO4  +  H2O2. 

When  barium  oxide,  BaO,  is  treated  with  sulphuric  acid  this  reac- 
tion takes  place : 

BaO  -f-  H2SO4  =  BaSO4  +  H2O. 

When  barium  dioxide  is  treated  with  hydrochloric  acid,  hydrogen 
dioxide  is  also  formed  thus: 

BaOa  +  2HC1  =  BaCl2  +  H2O2. 

[Compare  this  with  the  action  which  takes  place  when  hydrochlo- 
ric acid  acts  upon  manganese  dioxide.] 


CHAPTER   XX. 

THE    MAGNESIUM    FAMILY:    MAGNESIUM,    ZINC,   CAD- 

MIUM. 

OF  the  three  members  of  this  family,  magnesium  and 
zinc  are  by  far  the  best  known. 

Magnesium,  Mg  (At.  Wt.  24). — Magnesium  occurs  very 
widely  distributed  in  nature,  and  in  considerable  quanti- 
ties. Among  the  important  magnesium  minerals  are  mag- 
nesite,  which  is  the  carbonate  MgC03 ;  dolomite,  a  double 
carbonate  of  magnesium  and  calcium  ;  soapstone,  serpen- 
tine, and  meerschaum,  which  is  essentially  a  silicate  of  mag- 
nesium. Further,  there  are  many  silicates  which  contain 
magnesium,  among  them  being  asbestos  and  hornblende. 
The  metal  is  also  found  in  solution  in  many  spring-waters 
'  as  the  sulphate,  or  Epsom  salt. 

It  is  prepared  by  treating  magnesium  chloride  with 
sodium  at  a  high  temperature. 

It  is  a  silver-white  metal  with  a  high  lustre.  In  the  air 
it  changes  only  slowly,  but  gradually  becomes  covered  with 
a  layer  of  the  oxide.  When  heated  above  its  melting- 
point  in  the  air  it  burns  with  a  bright  flame,  forming  the 
white  oxide.  The  light  of  the  flame  is  very  efficient  in 
producing  certain  chemical  changes,  as  the  combination  of 
hydrogen  and  chlorine.  At  ordinary  temperatures  mag- 
nesium does  not  decompose  water;  at  100°  it  decomposes  it 


332  INTRODUCTION  TO  CHEMISTRY. 

slowly.  [Note  the  marked  difference  in  this  respect  be- 
tween magnesium  and  the  alkali  metals.] 

The  chief  compounds  of  magnesium  are  the  oxide,  MgG. 
called  magnesia  ;  the  sulphate,  MgS04  +  7H20,  commonl} 
called  Epsom  salt ;  the  carbonate,  MgCO, ;  the  silicates; 
and  the  chloride.  MgCl2. 

Magnesium  Oxide,  MgO. — This  compound  is  commonly 
called  magnesia.  A  fine  white  variety  is  made  by  heating 
precipitated  magnesium  carbonate ;  it  is  called  magnesia 
usta.  It  is  very  difficultly  soluble  in  water,  forming  with  it 
magnesium  hydroxide,  Mg02H2,  which  is  practically  insol' 
"able  in  water.  [What  difference  is  there  between  magne- 
sium and  calcium  in  this  respect  ?] 

Magnesium  chloride,  MgCl2,  is  of  special  interest  for 
the  reason  that  it  is  the  compound  from  which  the  metal 
magnesium  is  made.  It  is  prepared  by  dissolving  the  car- 
bonate in  hydrochloric  acid.  On  evaporating  this  solutior 
to  the  proper  concentration,  crystals  of  magnesium  chlo- 
ride containing  water  of  crystallization,  MgCla  -f  6HaO, 
are  deposited.  When  this  compound  is  heated  for  the 
purpose  of  drying  it,  the  larger  part  of  it  undergoes  de- 
composition, thus : 

MgCl2  +  H20  =  MgO  +  2H01. 

The  same  thing  takes  place  to  some  extent  on  heating 
calcium  chloride  with  water,  so  that  fused  calcium  chlo- 
ride is  always  slightly  alkaline  in  consequence  of  the  pres- 
ence of  lime,  or  calcium  oxide. 

Zinc,  Zn  (At.  Wt.  65). — Zinc  occurs  in  nature  in  combi- 
nation as  the  carbonate,  or  calamine,  ZnC03,  and  as  the  sul- 
phide, or  zinc  blende,  ZnS. 

It  is  prepared  by  mixing  the  oxide  with  charcoal  and 


ZING.  333 

heating  in  earthenware  retorts.     The  metal,  being  volatile, 
passes  over  and  is  condensed. 

Zinc  has  markedly  different  properties  at  different  temper- 
atures, At  ordinary  temperatures  it  is  quite  brittle;  at 
100-150°  it  can  be  rolled  out  in  sheets,  but  above  200°  it 
becomes  brittle  again.  In  dry  air  it  does  not  change. 
When  heated  in  the  air  it  takes  fire,  and  burns  with  a  bluish 
flame,  forming  zinc  oxide.  This  has  been  seen  in  the  ex- 
periments with  the  oxyhydrogen  blow-pipe.  It  dissolves  in 
all  the  common  acids,  usually  with  an  evolution  of  hydro- 
gen. In  the  case  of  nitric  acid,  however,  the  hydrogen 
acts  upon  the  nitric  acid,  reducing  it. 

Iron  is  sometimes  covered  with  a  layer  of  zinc.  Thus 
prepared,  it  forms  what  is  known  as  galvanized  iron.  Zinc 
is  a  constituent  of  brass. 

Zinc  oxide,  ZnO,  is  obtained  as  Flores  zinci  by  burning 
zinc,  and  by  heating  the  carbonate  or  nitrate  of  zinc.  It 
turns  yellow  when  heated,  but  on  cooling  becomes  white 
again. 

EXPERIMENT  154. — Heat  a  small  piece  of  zinc  on  charcoal 
in  the  oxidizing  flame  of  the  blow-pipe.  The  white  fumes 
of  zinc  oxide  (philosopher's  wool)  will  be  seen,  and  the 
charcoal  will  be  covered  with  a  film  which  is  yellow  while 
hot,  but  becomes  white  on  cooling.  [What  element  gives 
a  film  which  is  white  both  when  hot  and  when  cold?] 

Zinc  oxide  is  used  as  a  constituent  of  paint  under  the 
name  of  zinc  white. 

Zinc  Sulphate,  ZnS04  +  7H20,  is  commonly  called  white 
vitriol.     [In  what  experiments  has  zinc  sulphate  been  ob- 
tained?]    It  is  obtained  on  the  large  scale  by  heating  zinc 
sulphide  in  contact  with  the  air.     Under  these  circum 
stances,  the  sulphide  is  oxidized  : 


334  INTRODUCTION  TO  CHEMISTRY. 

ZnS  +  40  =  ZnS04. 

This  operation  is  known  as  roasting.  By  roasting  zinc 
sulphide  at  a  higher  temperature  it  is  converted  into  zinc 
oxide  : 

ZnS  +  30  =  ZnO  +  S02. 

Zinc  sulphate  is  also  formed  in  large  quantities  in  gal- 
vanic batteries  and  in  the  preparation  of  hydrogen. 

Zinc  chloride,  ZnCl2,  is  obtained  by  evaporating  a  water 
solution  of  the  substance  and  distilling  the  residue.  It  is 
an  oily  liquid  which  has  a  very  strong  affinity  for  water. 
On  evaporating  a  water  solution  a  part  of  the  chloride  un- 
dergoes decomposition,  just  as  magnesium  chloride  does, 
forming  the  oxide 


Zn012  +  HaO  =  ZnO  +  2H01. 

The  hydroxide,  sulphide,  carbonate,  and  phosphate  of 
zinc  are  insoluble  in  water. 

EXPERIMENT  155.  —  Produce  the  insoluble  compounds 
just  mentioned  and  express  the  reactions  by  means  of 
equations. 

[What  happens  on  bringing  together  solutions  of  sodium 
carbonate  and  zinc  sulphate?  ammonia  and  zinc  chloride? 
barium  chloride  and  zinc  sulphate?  lime-water  and  zinc 
sulphate?  What  color  has  zinc  sulphide?  Is  it  thrown 
down  when  the  solution  contains  dilute  hydrochloric  acid? 
Try  it.] 


CHAPTER  XXL 
THE  COPPER  FAMILY .  COPPER,  MERCURY,  SILVER. 

Copper,  Cu  (At.  Wt.  63.2). — Copper  occurs  in  nature 
in  the  uucombined  or  native  state  in  large  quanti- 
ties in  the  neighborhood  of  Lake  Superior,  in  the  United 
States,  and  in  Chili.  It  also  occurs  in  combination  with 
oxygen  as  ruby  copper,  which  is  the  oxide  Cu20;  and  with 
sulphur  and  iron  in  copper  pyrites. 

It  is  obtained  from  the  oxide  by  heating  it  with  charcoal. 
[This  reduction  has  been  illustrated  under  the  head  of 
carbon  (see  Experiment  88).]  It  is  also  obtained  from 
the  sulphides.  The  chemical  changes  involved  are  com- 
paratively complicated. 

Copper  is  a  bard  metal  of  a  reddish  color  and  metallic 
lustre.  It  does  not  change  in  dry  air,  but  in  moist  air  it 
gradually  becomes  covered  with  a  green  layer  of  a  carbon- 
ate of  copper.  Nitric  acid  dissolves  it,  copper  nitrate, 
Cu(N03)2,  being  formed,  and  oxides  of  nitrogen  evolved 
[explain  the  reaction];  hydrochloric  acid  does  not  act 
upon  it;  sulphuric  acid  acts  when  heated  with  the  metal; 
the  sulphate,  CuS04,  is  formed  and  sulphur  dioxide  given 
off  [explain  the  reaction].  Copper  cannot  decompose 
water,  even  when  water  vapor  is  passed  over  the  metal 
heated  to  red  heat.  [Compare  with  the  conduct  of  the  mem- 
bers of  the  potassium,  calcium,  and  magnesium  families.] 

It  is  precipitated  from  solutions  of  its  salts  by  zinc,  iron, 
and  some  other  metals,  and  by  an  electric  current. 


336  INTRODUCTION  TO   CHEMISTRY. 

EXPERIMENT  156. — Into  a  neutral  solution  of  copper 
sulphate  insert  a  strip  of  zinc.  The  zinc  will  become  cov- 
ered with  a  layer  of  copper,  and  zinc  will  pass  into  solution 
as  zinc  sulphate.  The  zinc  simply  displaces  the  copper  in 
this  case,  as  it  displaces  hydrogen  from  sulphuric  acid : 

Zn  -f  CuS04  =  ZnS04  +  Cu; 
Zn  +  H2S04  =  ZnS04  +  H2. 

Perform  a  similar  experiment,  using  a  strip  of  sheet- 
iron  instead  of  the  zinc.  [What  is  the  result?]  To  those 
who  first  performed  this  experiment  the  iron  appeared  to  be 
changed  to  copper.  [How  would  you  go  to  work  to  deter- 
mine whether  the  iron  is  changed  to  copper  or  not?] 

The  deposition  of  metallic  copper  from  solutions  of  its 
salts  is  extensively  utilized  in  copper-plating.  The  object 
to  be  covered  with  copper  is  hung  in  a  solution  of  copper 
sulphate  and  connected  with  one  pole  of  a  galvanic  battery, 
the  other  pole  being  also  in  the  solution.  Decomposition 
takes  place,  and  a  layer  of  copper  is  deposited  on  the  ob- 
ject. 

Brass  is  a  mixture  of  1  part  of  zinc  and  2  parts  of  cop- 
per. Bell-metal  and  bronze  are  mixtures  of  copper  and 
tin.  Such  mixtures  of  metals  which  are  made  by  melting 
them  together  are  called  alloys.  It  appears  that  some  alloys 
are  closely  allied  to  chemical  compounds. 

Among  the  more  common  compounds  of  copper  are  the 
oxides  Cu20  and  CuO,  the  sulphate  CuS04,  and  the  sul- 
phide CuS. 

Copper  has  the  power  to  form  two  distinct  series  of  com- 
pounds, of  which  the  following  examples  will  serve  as 
illustrations: 


CUPMOUS  AMD  CUPRIC  COMPOUNDS.  337 

CuCl,  Ou01f; 
CuBr,  CuBr,; 
CuaO,  CuO. 

Those  compounds  which  are  of  the  first  order  corre- 
sponding to  the  chloride,  CuCl,  are  called  cuprous  com- 
pounds. Thus,  CuCl  is  cuprous  chloride;  Cn?0,  cuprous 
oxide,  etc.  On  the  other  hand,  compounds  of  the  second 
order  are  called  cupric  compounds.  Thus,  CuCl,  is  cupric 
chloride;  CuO,  cupric  oxide,  etc.  It  has  been  suggested 
that  perhaps  the  formula  of  the  simpler  cuprous  com- 
pounds like  CuCl,  etc.,  should  be  doubled,  and  written 
Cu3Cl2,  Cu2Br2,  etc.  This  suggestion  has  its  origin  in  the 
valence  conception.  In  cupric  chloride,  CuCl,,  and  cu- 
pric oxide,  CuO,  copper  is  evidently  bivalent;  whereas  if 
the  formulas  of  the  cuprous  compounds  are  the  simple  ones 
CuCl,  CuI,  etc.,  then  in  them  copper  is  univalent.  If, 
however,  cuprous  chloride  is  Cu2Cl2,  it  may  be  that  in  it 
the  copper  is  bivalent.  It  is  only  necessary  to  assume  that 
in  the  molecule  of  cuprous  chloride  two  atoms  of  copper 
are  combined  as  represented  thus  : 

Cu— 


If  then  each  of .  the  copper  atoms  should  combine  with  a 
chlorine  atom,  the  compound  would  have  the  formula 
Cu2Cl3.  Unfortunately,  we  have  no  experimental  means 
of  showing  whether  the  molecule  of  cuprous  chloride  is 
more  probably  Cu2Cl2,  or  CuCl,  so  that  the  above  reason- 
ing is  purely  speculative.  It  is  better,  therefore,  for  the 
present  to  keep  to  the  simpler  formula.  Whatever  the 
22 


338  INTRODUCTION  TO  CHEMISTRY. 

explanation  may  be,  it  is  unquestionably  a  fact  that  there 
are  two  series  of  salts  of  copper,  in  one  of  which  there  is 
relatively  half  as  much  copper  as  in  the  other.  Mercury, 
iron,  and  some  other  metals  present  similar  phenomena. 

Cuprous  oxide,  Cu20,  is  found  in  nature  as  ruby  copper^ 
and  is  formed  when  copper  is  heated  in  contact  with  the 
air.  It  is  a  bright-red  insoluble  substance. 

Cupric  oxide,  CuO,  is  obtained  by  heating  copper  to  red- 
ness in  contact  with  the  air,  or  by  heating  the  nitrate.  It 
is  also  formed  when  caustic  soda  or  potash  is  added  to  a 
boiling-hot  solution  of  a  copper  salt.  If  the  solution  is 
cold,  blue  cupric  hydroxide,  Cu02H2,  is  precipitated,  but 
Ahis  easily  loses  water,  particularly  if  the  solution  is  heated. 
'The  reactions  which  take  place  are  : 


CuS04  +  2NaOH  =  Cu02Ha  +  JSTa2S04,  and 
Cu0H=CuO      H0. 


22 


EXPERIMENT  157.  —  Add  some  caustic  soda  or  potash  to 
a  small  quantity  of  a  cold  solution  of  copper  sulphate  in  a 
test-tube.  Heat  and  notice  the  change  from  blue  to  black. 

Copper  Sulphate,  CuS04  -f  5H20.  —  This  salt  is  manu- 
factured on  a  large  scale  and  is  commonly  known  by  the 
name  "blue  vitriol."  [What  salt  is  called  "white  vitriol?"] 
It  forms  large  blue  crystals,  which,  when  heated,  lose  water 
and  become  colorless.  The  colorless  substance  becomes 
blue  again  in  contact  with  water. 

Copper  Sulphide,  CuS,  is  a  black  substance  which  is 
formed  by  passing  hydrogen  sulphide  through  a  solution 
of  a  copper  salt,  or  by  adding  a  soluble  sulphide,  as  potas- 
sium sulphide  or  ammonium  sulphide  to  such  a  solution. 


MERCURY.  339 

EXPERIMENT  158. — Treat  a  dilute  solution  of  copper  sul- 
phate with  hydrogen  sulphide,  with  ammonium  sulphide, 
with  potassium  or  sodium  sulphide. 

Mercury,,  Hg  (At.  Wt.  200). — Mercury  occurs  native 
as  drops  enclosed  in  rocks,  though  principally  in  combina- 
tion with  sulphur  as  cinnabar,  HgS.  It  is  obtained  by 
roasting  cinnabar,  when  vapors  of  mercury  and  sulphur 
dioxide  are  given  off.  The  mercury  is  condensed  in  ap- 
propriate vessels.  It  is  a  silver-white  metal  of  a  high  lustre. 
At  ordinary  temperature  it  is  liquid,  though  it  becomes 
solid  at— 39°.5,  Its  specific  gravity,  water  being  the 
standard,  is  13.5959.  It  does  not  change  in  the  air  at  or- 
dinary temperatures.  It  is  insoluble  in  hydrochloric  acid 
and  cold  sulphuric  acid  [Try  each.]  It  dissolves  in  hot 
concentrated  sulphuric  acid,  and  is  easily  soluble  in  nitric 
acid.  [Try  each.]  The  vapor  of  mercury  is  very  poisonous. 

With  other  metals  it  forms  alloys  called  amalgams.  In 
ordinary  galvanic  batteries  the  zinc  plates  are  treated  with 
mercury,  and  thus  covered  with  a  layer  of  zinc  amalgam 
which  protects  them  from  the  action  of  the  acids  used. 

Among  the  more  common  compounds  of  mercury  are 
the  oxide,  HgO  ;  the  two  chlorides,  mercurous  chloride, 
HgOl,  and  mercuric  chloride,  HgCl2 ;  the  two  iodides, 
mercurous  iodide,  Hgl,  and  mercuric  iodide,  HgI2 ;  and  the 
sulphide,  HgS. 

Mercuric  oxide,  HgO,  is  the  red  substance  which  was 
used  in  one  of  our  first  experiments  for  the  purpose  of  pre- 
paring oxygen.  It  is  formed  when  mercury  is  heated  for 
some  time  near  its  boiling-point  in  contact  with  the  air, 
and  is  made  by  heating  the  nitrate. 

Mercurous  chloride,  HgCl,  is  commonly  known  by  the 
name  calomel.  It  is  precipitated  when  a  soluble  chloride 


340  INTRODUCTION  TO  CHEMISTRY. 

or  hydrochloric  acid  is  added  to  a  solution  of  any  mercu- 
rous  salt.  It  is  manufactured  by  subliming  an  intimate 
mixture  of  mercuric  chloride  and  mercury  . 

HgOl,  +  Hg  =  SHgCL 

It  is  a  white  substance,  insoluble  in  water,  which  finds  ex- 
tensive application  in  medicine. 

Mercuric  chloride,  HgCl.^  commonly  called  corrosive  sub- 
limate, is  manufactured  on  the  large  scale  by  subliming  an 
intimate  mixture  of  mercuric  sulphate  and  common  salt: 


HgS04  +  2NaCl  =  Na,S04  +  Hg013. 

It  is  a  white  substance,  soluble  in  water.  It  is  extremely 
poisonous,  and  prevents  the  decay  of  organic  substances. 

Mercuric  sulphide,  HgS,  occurs  in  nature  as  cinnabar  in 
the  form  of  red  crystals  or  crystalline  masses.  When  pre- 
pared artificially  by  rubbing  mercury  and'  flowers  of  sul- 
phur together  or  by  passing  hydrogen  sulphide  through  a 
solution  containing  a  mercury  salt,  it  is  a  Hack  powder. 
When  sublimed  this  powder  yields  red  crystals. 

It  will  be  noticed  that  of  the  two  chlorides  only  mercu- 
rous  chloride  is  insoluble  in  water.  If  any  mercuroussalt 
is  present  in  a  solution,  mercurous  chloride  will  be  thrown 
down  by  adding  a  chloride  or  hydrochloric  acid;  whereas  if 
the  salt  is  a  mercuric  salt  the  addition  of  a  chloride  or  hy- 
drochloric acid  will  produce  no  precipitate. 

Silver,  Ag  (At.  Wt.  108).  —  Silver  occurs  native;  in 
combination  with  sulphur  ;  and  with  sulphur  and  other 
metals.  Small  quantities  of  silver  sulphide  are  found  in 
almost  all  varieties  of  galenite  or  lead  sulphide.  It  occurs 
more  rarely  as  the  chloride,  bromide,  and  iodide. 


SlLVKll.  341 

Much  of  the  silver  in  use  is  obtained  from  galenite.  This 
mineral  is  treated  in  such  a  way  as  to  cause  the  separation 
of  the  lead  (see  Lead),  and  the  silver  is  separated  from  sul- 
phur at  the  same  time.  But  it  is  dissolved  in  a  large 
quantity  of  lead,  and  the  problem  which  presents  itself  to 
the  metallurgist  is  how  to  separate  the  small  quantity  of 
silver  from  the  large  quantity  of  lead.  This  is  accomplished 
by  melting  the  mixture  and  allowing  it  to  cool  until  crys- 
tals appear.  These  are  almost  pure  lead.  They  are  dipped 
out  and  the  liquid  left  is  again  treated  in  the  same  way.  By 
this  means  there  is  finally  obtained  a  product  which  is  rich 
in  silver  but  which  still  contains  lead.  This  is  heated  in 
appropriate  vessels  in  contact  with  the  air,  when  the  lead 
is  oxidized,  while  the  silver  remains  in  the  metallic  state. 

Some  ores  of  silver  are  treated  in  another  way  known  as 
the  amalgamation  process.  The  ores  are  mixed  with  com- 
mon salt  and  roasted,  when  the  silver  is  obtained  in  the 
form  of  the  chloride.  The  mass  is  then  treated  with  iron 
and  water,  when  this  reaction  takes  place  : 

SAgCl  +  Fe  =  FeCl2  +  2Ag. 

The  mixture  is  next  treated  with  mercury,  which  forms 
an  amalgam  with  the  silver.  When  this  amalgam  is  heated 
the  mercury  passes  over,  while  the  silver  remains  behind. 

The  methods  described  above  illustrate  the  applications 
of  chemistry  to  the  solution  of  important  problems. 

Silver  is  a  white  metal  with  a  high  lustre.  It  is  not  acted 
upon  by  air,  oxygen,  or  water.  Sulphur  acts  readily  upon  it, 
causing  it  to  blacken  superficially,  the  black  coating  being 
silver  sulphide.  Silver  is  not  dissolved  by  hydrochloric 
acid,  but  is  dissolved  easily  by  concentrated  sulphuric  acid 
and  dilute  nitric  acid. 


342  INTRODUCTION  TO  CHEMISTRY. 

The  silver  which  is  used  for  coins  and  most  other  purposes 
is  an  alloy  with  copper,  the  pure  metal  being  too  soft.  The 
alloy  usually  contains  from  7J-  to  10  per  cent  of  copper. 
Other  metals  covered  with  a  layer  of  silver,  deposited  by 
the  action  of  an  electric  battery,  are  said  to  be  silver-plated. 

The  principal  compounds  of  silver  are  the  chloride,  AgCl; 
bromide,  AgBr;  iodide,  Agl;  and  nitrate,  AgN03. 

Silver  nitrate,  AgN03,  is  known  also  by  the  name  ' '  lunar 
caustic."  It  is  prepared  by  dissolving  silver  in  dilute 
nitric  acid. 

EXPERIMENT  159. — Dissolve  a  ten  or  twenty-five  cent 
piece  in  dilute  nitric  acid.  [What  action  takes  place  ?] 
Dilute  the  solution  to  200  to  300  cc.  with  water.  [What  is 
the  color  of  the  solution  ?  What  does  this  indicate  ?  Does 
this  color  prove  the  presence  of  copper  ?]  Add  a  solution 
of  common  salt  until  it  ceases  to  produce  a  precipitate. 
[What  is  the  chemical  change  ?]  Filter  off  the  white  silver 
chloride  and  carefully  wash  with  hot  water.  Dry  the  pre- 
cipitate on  the  filter,  by  placing  the  funnel  with  the  filter 
and  precipitate  in  an  air-bath  heated  to  about  110°.  Re- 
move the  precipitate  from  the  filter  and  put  it  into  a  porce- 
lain crucible.  Heat  gently  with  a  small  flame  until  the 
chloride  is  melted.  Cut  out  a  piece  of  sheet-zinc  large 
enough  to  cover  the  bottom  of  the  crucible,  and  lay  it  on 
the  silver  chloride.  Now  add  a  little  water  and  a  few  drops 
of  dilute  sulphuric  acid,  and  let  the  whole  stand  for  twenty- 
four  hours.  The  silver  chloride  is  reduced  to  silver,  and 
zinc  chloride  is  formed  : 

Zn  +  SAgCl  =  ZnCla  +  2Ag. 

Take  out  the  piece  of  zinc  and  wash  the  silver  with  a 
little  dilute  sulphuric  acid,  and  then  with  water.  Heat  a 


PHOTOGRAPHY.  343 

small  piece  of  the  metal  on  charcoal  with  the  blow-pipe 
flame  until  it  melts  and  forms  a  bead.  Dissolve  the  silver 
in  dilute  nitric  acid  and  evaporate  to  dryness  in  the  water- 
bath,  so  that  the  excess  of  nitric  acid  is  driven  off.  •  Dis- 
solve the  residue  in  water  and  put  the  solution  either  in  a 
bottle  of  dark  glass  or  one  wrapped  in  dark  paper. 

EXPERIMENT  160. — To  a  few  cubic  centimetres  of  water 
in  a  test-tube  add  5  to  10  drops  of  the  solution  of  silver 
nitrate  just  prepared.  To  this  dilute  solution  add  a  little 
of  a  dilute  solution  of  sodium  chloride.  The  curdy  white 
precipitate  is  silver  chloride.  Stand  it  aside  where  the 
light  can  shine  upon  it,  and  notice  the  change  of  color 
which  gradually  takes  place.  In  the  same  way  make  the 
bromide  by  adding  potassium  bromide,  and  the  iodide  by 
adding  potassium  iodide  to  silver  nitrate. 

It  will  be  seen  from  the  last  experiments  that  the 
chloride,  bromide,  and  iodide  of  silver  are  insoluble  in 
water  and  are  changed  by  light.  The  art  of  photography 
is  based  upon  the  changes  which  certain  compounds, 
especially  salts  of  silver,  undergo  when  exposed  to  the  light. 
A  plate  of  glass  is  covered  in  the  dark  with  a  thin  layer  of 
a  salt  of  silver.  The  plate  is  then  exposed  in  the  camera 
to  the  action  of  the  light  from  some  object  to  be  photo- 
graphed. The  salt  is  changed  when  it  is  acted  upon  by 
the  light,  while  where  there  is  no  light  it  is  not  acted  upon. 
An  image  of  the  object  towards  which  the  plate  was 
directed  is  thus  left  on  the  plate. 

Silver  is  precipitated  from  solutions  of  its  salts  by  zinc, 
copper,  mercury,  and  other  metals. 

EXPERIMENT  161.— To  a  solution  of  silver  nitrate  con- 
taining about  5  grams  of  the  salt  in  100  cc.  water  add  a 
few  drops  of  mercury,  and  let  it  stand.  In  a  few  days 


344  INTRODUCTION  TO  CHEMISTRY. 

the  silver  will  be  deposited  in  the  form  of  delicate  crystals, 
The  formation  is  called  the  "silver  tree." 

The  oxide,  chloride,  bromide,  iodide,  sulphide,  car- 
bonate, and  phosphate  of  silver  are  insoluble  in  water. 
[Verify  these  statements.] 

[What  takes  place  when  hydrochloric  acid  is  added  to  a 
solution  of  a  silver  salt?  When  silver  nitrate  is  added  to 
barium  chloride?  When  ammonium  carbonate  is  added  to 
silver  nitrate?  When  disodium  phosphate  is  added  to 
silver  nitrate?  In  this  case,  normal  silver  phosphate, 
Ag3P04,  is  formed,  and  some  nitric  acid  is  set  free.] 

Silver  forms  mostly  those  gpjnpounds  which  are  analo- 
gous to  the  cuprous  and  mercurous  salts,  and  not  those 
which  are  analogous  to  the  cupric  and  mercuric  salts.  There 
is,  however,  an  oxide,  Ag20,  and  another,  AgO,  corre- 
sponding to  mercurous  and  mercuric  oxides. 

The  Specific  Heat  of  Elements  as  a  means  of  Determining 
their  Atomic  Weights. — The  question  naturally  suggests 
itself,  How  are  the  atomic  weights  determined  in  the  case 
of  elements  like  silver,  copper,  etc.,  which  cannot  be  con- 
verted into  the  form  of  vapor,  and  which  do  not  yield  com- 
pounds which  can  be  converted  into  vapor?  It  will  be  re- 
membered that  most  of  the  atomic  weights  with  which  we 
have  thus  far  had  to  deal,  as  those  of  oxygen,  chlorine, 
nitrogen,  etc.,  are  determined  by  a  consideration  of  the 
specific  gravity  of  the  vapors  of  the  compounds  of  these 
elements.  We  determine  the  relative  weights  of  equal 
volumes  of  these  gases  or  vapors,  and  then,  assuming  that 
these  weights  express  the  relative  weights  of  the  molecules 
of  the  compounds,  we  select  the  smallest  weight  of  the  ele- 
ment occurring  in  any  compound  as  the  atomic  weight. 
[Refer  back  and  carefully  read  the  chapter  relating  to  the 


SPECIFIC  HEAT. 

Atomic  Theory  and  Avogadro's  Hypothesis.]  But  how- 
ever valuable  this  method  may  be,  it  does  nofc  help  us  in 
the  case  of  solid  elements,  which  cannot  be  converted  into 
vapor,  and  which  do  not  yield  compounds  capable  of  con- 
version into  vapor.  In  such  cases  the  effect  of  heat  upon 
the  elements  is  of  assistance.  It  has  been  found  that  when 
equal  weights  of  different  elements  are  exposed  to  exactly 
the  same  source  of  heat,  they  require  different  lengths  of 
time  to  become  heated  to  the  same  temperature.  Given 
exactly  the  same  heating  power,  it  requires  32  times  as 
long  to  raise  the  -temperature  of  a  pound  of  water 
.10,  20,  or  30  degrees  as  it  does  to  raise  a  pound  of  mer- 
cury the  same  number  of  degrees;  or  it  takes  32  times  as 
much  heat  to  raise  a  pound  of  water  10,  20,  or  30  degrees 
as  it  does  to  raise  a  pound  of  mercury  the  same  num- 
ber of  degrees.  The  quantity  of  heat  required  to  raise 
the  temperature  of  a  certain  weight  of  a  substance  one  de- 
gree -as  compared  with  the  quantity  of  heat  required  to 
raise  the  temperature  of  the  same  weight  of  water  one  de- 
gree is  called  the  specific  heat  of  the  substance.  Thus, 
from  what  was  said  above,  the  specific  heat  of  mercury  is 
^,  or,  in  decimals,  0.03332.  In  a  similar  way  it  can  be 
shown  that  the  specific  heat  of  gold  is  0.03244;  of  zinc, 
0.0955;  of  silver,  0.057;  of  copper,  0.0952.  But  these 
figures  bear  a  remarkable  relation  to  the  combining 
weights  found  by  means  of  analysis.  Thus,  taking  the 
above  elements,  we  have  : 

Specific  Heat.  Comb.  Weight. 

Mercury 0.03332, 200 

Gold 0.03244 196.2 

Zinc 0.0955   65 

Silver 0.057     108 

Copper 0.0952 63.2 


346  INTRODUCTION  TO  CHEMISTRY. 

Calculation  will  show  that  the  specific  heat  of  these  ele- 
ments is  approximately  inversely  proportional  to  their 
combining  weights.  Thus 

0.03332    :       0.057       ::         108  T        200 

Sp.  Ht.  of  Hg.        Sp.  Ht.  of  Ag.        Comb.  Wt.  of  Ag.        Comb.  Wt.  of  Hg. 

And  the  same  is  true  in  the  other  cases.  Or  the  relation 
may  be  stated  in  another  way,  viz. :  The  product  of  the 
specific  heat  of  any  element  multiplied  by  its  combining 
weight  is  the  same  in  all  cases.  The  product  is  about  6.25. 
It  is  believed  that  the  quantities  of  the  elements  to  which 
this  law  refers  are  in  reality  the  atomic  weights,  and  we 
therefore  accept  the  law  known  as  the  law  of  Dulong  and 
Petit,  which  is  this  : 

The  atomic  weight  of  an  element  multiplied  by  its  specific 
heat  is  a  constant  equal  to  about  6,25. 

There  are  some  exceptions  to  the  law,  but  these  cannot 
be  discussed  at  this  time.  "With  its  imperfections  it  is  of 
value,  and  is  now  recognized  as  furnishing  a  valuable  means 
of  determining  atomic  weights.  If  A  represents  the  atomic 
weight,  and  S  the  specific  heat,  then,  according  to  the  law 
of  Dulong  and  Petit,  Ax  S  =  6.25  nearly,  and  A  = 

6  25 

—•a—      By  determining  the  specific  heat  of  an  element,  and 

dividing  it  into  6.25,  a  figure  will  be  obtained  near  the 
atomic  weight.  By  careful  analysis  of  compounds  of  the 
element  the  figure  can  be  determined  more  accurately.* 

6.25 
*  The  mere  committal  to  memory  of  the  rule  A  —  -g-  without  an 

understanding  of  the  facts  from  which  it  is  deduced  is  of  no  value. 
In  the  early  stages  of  his  course  in  chemistry  the  student  should  not 
be  allowed  to  repeat  the  rule  without  a  careful  statement  in  his  own 
words  of  its  meaning. 


CHAPTER  XXII. 

THE  ALUMINIUM  FAMILY:  ALUMINIUM,  GALLIUM,  IN- 
DIUM, THALLIUM,  SCANDIUM,  YTTRIUM,  LANTHA- 
NUM, AND  YTTERBIUM. 

THE  only  element  of  this  family  which  need  be  consid- 
ered now  is  aluminium.  This  is  an  extremely  important 
element,  which  occurs  very  widely  distributed  in  nature. 

Aluniinium,  Al  (At.  Wt.  27). — Among  the  many  impor- 
tant and  widely  distributed  minerals  which  contain  alu- 
minium are  feldspar,  granite,  mica,  and  cryolite.  Clay  is 
aluminium  silicate. 

Aluminium  is  prepared  by  treating  the  chloride  with 
metallic  sodium.  [How  is  magnesium  prepared  ?  How 
sodium  ?]  Its  color  is  like  that  of  tin,  and  it  has  a  strong 
lustre.  It  is  very  strong  and  yet  malleable.  It  is  lighter 
than  most  metals  in  common  use,  its  specific  gravity  being 
2.7,  while  that  of  iron  is  7.8,  that  of  silver  10.57,  and  that 
of  tin  7.3.  Further,  it  does  not  chang;e_in  dry  or  moist  air. 
These  properties  give  it  great  value,  and  it  is  only  the  fact 
that  it  cannot  be  prepared  cheaply  from  the  compounds  found 
in  nature  that  prevents  its  wide-spread  use.  The  discovery 
of  a  method  by  which  aluminium  could  be  prepared  eco- 
nomically would  be  of  the  highest  importance.  It  will  only 
be  made  through  a  thorough  study  of  the  laws  of  chemistry, 
and  will  come  with  a  clearer  understanding  of  the  science. 
Among  the  more  important  compounds  of  aluminium  are 
aluminium  oxide,  A1203;  aluminium  hydroxide,  A10SH3; 
the  alum^-  the  silicates;  and  the  chloride,  A12C16  or  A1C13. 

Aluminium  Oxide,  A1263. — This  compound  occurs  rarely 
in  nature  in  the  form  of  ruby,  sapphire,  and  corundum. 


848  INTRODUCTION  TO  CHEMISTRY. 

It  is  very  hard,  and  as  emery  is  used  for  polishing.     It  is 
made  artificially  by  heating  the  hydroxide,  A103H3 : 

2A103HS  =  A1203  +  3H20. 

Aluminium  Hydroxide,  A108H3. — This  compound  is 
found  in  nature  in  crystallized  form  as  hydrargillite.  It  is 
precipitated  when  ammonia  is  added  to  a  solution  of  alu- 
mimumjul^hate : 

A12(S08)3  +  6NH4OH  =  3(NH4)2S04  +  2A103H3. 

It  forms  a  gelatinous  mass  which  is  difficult  to  filter. 
[Precipitate  some  from  a  solution  of  ordinary  alum.]  The 
hydroxide  is  soluble  in  acids  and  in  alkalies.  In  the  former 
case  salts  are  formed  in  which  the  hydroxide  plays  the  part 
of  a  base;  in  the  latter  it  acts  like  an  acid.  The  salts 
formed  with  the  alkalies  are  called  aluminates.  In  alu- 
minium salts  one  atom  of  the  metal  replaces  three  atoms  of 
hydrogen;  thus,  aluminium  nitrate  is  A1(N03)3;  the  sul- 
phate, A12(S04)3,  etc.  In  the  aluminates  the  three  hydro- 
gen atoms  of  the  hydroxide  are  replaced  by  metal;  thus, 
potassium  aluminate  is  A103KS,  and  sodium  aluminate, 
AlO.Nn... 

EXPERIMENT  162. — Precipitate  some  aluminium  hydrox- 
ide from  a  dilute  solution  of  alum,  by  means  of  caustic 
potash,  and  continue  to  add  the  latter  slowly,  when  the 
precipitate  will  dissolve.  Do  the  same  with  caustic  soda. 

Aluminium  hydroxide,  A103H3,  loses  water  when  heated, 
and  a  compound  of  the  formula  A102H  is  formed: 

A103H3  =  A102H  +  H20. 

This  compound  is  found  in  nature  as  the  mineral  dia- 
spore.  It  has  acid  properties  and  forms  extremely  stable 
salts,  several  of  which  are  found  in  nature.  Spinel  is 


ALUMS,  ETC.  349 

magnesium  aluminate  (A102)2Mg.  The  formation  of  the 
hydroxides  A103H3  and  A102H,  and  of  salts  derived  from 
each,  indicates  some  analogy  between  aluminium  and  boron. 
On  the  other  hand,  the  power  to  replace  the  hydrogen  of 
acids  is  not  possessed  by  boron.  [Kefer  back  to  Boron. 
Eead  again  what  is  said  about  it,  and  note  particularly  the 
points  of  resemblance  and  difference  with  aluminium.] 

Alums. — Aluminium  sulphate  forms  complex  compounds 
with  the  sulphates  of  the  alkali  metals,  all  of  which  crystal- 
lize beautifully.  Potassium  alum  is  the  best  known  of 
these.  It  may  be  regarded  as  derived  from  2  molecules  of 
sulphuric  acid  by  the  replacement  of  3  atoms  of  hydrogen 
by  1  atom  of  aluminium,  and  the  fourth  by  1  atom  of  po- 
tassium; thus,  A1K(S04)2.  The  crystals  always  contain  12 
molecules  of  water,  the  complete  formula  being  A1K(S04), 
+  12H20.  Similarly,  sodium  alum  is  AlN~a(S04)2  + 
12H20,  and  ammonium  alum  A1NH4(S04)2  -f  12H20. 

Aluminium  Silicates. — The  silicate  of  aluminium  occurs 
in  nature  in  enormous  quantities,  in  combination  with 
other  silicates  forming  some  of  the  most  important  min- 
erals. The  most  abundant  of.  these  is  ordinary  feldspar, 
which  is  a  silicate  of  aluminium  and  potassium,  AlKSi3Q^, 
Clay,  which  in  pure  form  is  known  as  Kaoline,  is  aluminium 
silicate  in  combination  with  water,  Al4(Si04)3  -f-  4H20.  It 
is  derived  from  the  acid  H4Si04.  Kaoline  is  used  for 
making  porcelain.  Ordinary  clay  is  used  for  making 
bricks  and  for  other  purposes. 

Ultramarine. — The  substance  known  as  lapis  lazuli  con- 
sists of  a  silicate  of  aluminium  and  sodium,  together  with  a 
polysulphide  of  sodium.  The  coloring  matter  obtained  by 
powdering  it  was  formerly  very  expensive,  but  it  is  now 
made  artificially  by  the  ton,  and  the  color  of  the  artificially 


350  INTRODUCTION  TO  CHEMISTRY. 

prepared  substance  is  even  more  beautiful  than  that  of  the 
natural. 

With  weak  acids  aluminium  forms  no  salts.  There  is, 
for  example,  no  carbonate.  The  sulphide  is  so  unstable 
that  it  decomposes  into  the  hydroxide  and  hydrogen  sul- 
phide when  exposed  to  moist  air.  When  a  soluble  hydroxide 
is  added  to  a  solution  of  a  salt  of  aluminium,  the  insoluble 
hydroxide  is  precipitated;  but,  as  this  has  acid  properties, 
it  is  dissolved  in  an  excess  of  either  caustic  soda  or  caustic 
potash.  Owing  to  the  weak  basic  properties  of  the  hy- 
droxide, sodium  carbonate  and  other  soluble  carbonates 
precipitate,  not  the  carbonate,  but  the  uncombined  hy- 
droxide. 

/    EXPERIMENT   163, — Add  a  dilute  solution  of  sodium 
\  carbonate  to  a  dilute  solution  of  alum.     The  precipitate  is 
the  hydroxide : 

2A1K(S04)2  +  3Na2C03  +  3H20 

=  K2S04  +  3Na2S04  +.300,  +  2A108H8. 

Filter  off  and  show  that  the  precipitate  is  not  the  car- 
bonate. Try  the  same  experiment  with  ammonium  and 
potassium  carbonates. 

When  an  aluminium  salt  in  solution  is  treated  with  am- 
monium sulphide,  the  hydroxide  is  precipitated.     Even  if 
the  sulphide  were  formed  it  would  be  decomposed  into  the 
hydroxide  and  hydrogen  sulphide  by  water, 
r  EXPERIMENT  163  a. — Add  ammonium  sulphide  to  a  solu- 
tion of  alum.     The  precipitate  is  aluminium  hydroxide  : 
2A1K(S04)2  +  3(NH4)2S  +  6H20 

=  3(NH4)2S04  +  K2S04  +  3H2S  +  2A103H3. 

The  other  members  of  the  aluminium  family  need  not 
be  considered  here.  Two  of  them,  gallium  and  scandium, 
have  only  recently  been  discovered. 


CHAPTEE  XXIII. 
THE  IRON  FAMILY  :  IRON,  COBALT,  NICKEL. 

Iron,  Fe  (At.  Wt.  56). — At  the  present  time  it  is  un- 
doubtedly true  that  iron  is  the  most  important  metal  for 
man.  It  is  not  improbable,  however,  that  in  the  future 
aluminium  may  take  its  place  for  many  purposes,  though 
there  appears  to  be  no  immediate  prospect  of  this  inter- 
"erence  with  the  iron  industry. 

Iron  occurs  in  the  form  of  the  oxides,  IJe^O^jand  Fe203 ; 
,s  the  carbonate^  FeCQa ;  in  combination  with  sulphur  as 
ron  pyrites,  KeS2;  and  as  silicates  and  hydrated  oxides,  or 
tydroxides. 

The  extraction  of  iron  from  its  ores  is  theoretically 
imple,  the  essential  steps  in  the  process  being  : 

(1)  The  conversion  of  the  ore  into  the  oxides,  unless  the 
>xides  are  themselves  found. 

This  is  accomplished  by  roasting  them.  If  sulphides  are 
roasted  the  sulphur  passes  off  as  sulphur  dioxide,  and  the 
iron  remains  as  the  oxide.  In  roasting,  further,  water  is 
driven  off  and  the  carbonate  is  decomposed  into  oxide  and 
carbon  dioxide. 

(2)  Reduction  of   the  oxides  by  means  of  charcoal  or 
coke. 

This  is  accomplished  by  mixing  the  ore  with  the  reduc- 
ing agent  and  heating  in  a  blast-furnace.  As  the  iron  is 
reduced  it  sinks  into  the  lower  part  of  the  furnace,  which 
is  called  the  crucible,  and  is  drawn  off  in  the  liquid  condi- 
tion. 


352  INTRODUCTION  TO  CHEMISTRY. 

The  iron  drawn  off  from  the  crucible  is  called  pig-iron. 
It  is  always  impure,  containing  carbon,  phosphorus,  sulphur, 
silicon,  etc.  In  this  condition  it  is  brittle  and  easily  fusi- 
ble. It  is  used  for  casting,  and  is  known  as  cast  iron. 
When  the  carbon,  silicon,  and  phosphorus  are  removed  the 
iron  is  very  tough  and  malleable.  This  is  wrought  iron. 
Cast  iron  is  converted  into  wrought  iron  in  one  of  two 
ways  : 

(1)  By  melting  it  and  blowing  air  into  the  molten  mass. 
The  carbon,  phosphorus,  and  silicon  are  thus  oxidized  and 
gotten  rid  of.     This  process  is  known  &s  puddling. 

(2)  By  mixing  cast  iron  with  some  of  the  purer  ores  and 
heating  to  a  high  temperature,  when  the  carbon,  phospho- 
rus, etc.,  are  oxidized  by  the  oxygen  of  the  ores.     This 
process  is  called  cementation. 

Steel  contains  more  carbon  than  wrought  and  less  than 
cast  iron.  There  are  two  methods  by  which  it  is  made  : 

(1)  Wrought  iron  is  heated  with  charcoal  or  with  iron 
containing   carbon.     This   is   known   as   the    cementation 
process. 

(2)  Cast  iron  is  melted  in  a  large  vessel  called  a  con- 
verter, and  then  partly  oxidized  by  currents  of  air  forced 
into  the  mass.     Cast  iron  is  now  added,  and  steel  contain- 
ing any  desired  proportion  of  carbon  thus  made.     This  is 
known  as  the  Bessemer  process. 

The  differences  between  cast  iron,  wrought  iron,  and 
steel  are  very  marked.  They  may  be  summed  up  in  a  few 
words  as  follows  : 

Cast  iron  melts  easily,  is  brittle  when  cold,  and  is  not 
as  hard  as  steel. 

Steel  has  the  property  of  becoming  extremely  hard  and. 
brittle,  when  heated  and  suddenly  cooled.  When 


COMPO  UNDS  OF  IRON.  353 

tiously  heated  and  allowed  to  cool  slowly  it  is  rendered 
j^lasjic.     This  process  is  called  tempering. 

Wrought  iron  is  tough  and  malleable. 

Pure  iron  is  almost  unknown.  It  is  a  white  metal.  In 
moist  air  it  rusts;  that  is,  it  becomes  covered  with  a  layer 
of  oxide  and  hydroxide  which  is  formed  by  the  action  of 
the  air  and  water. 

Iron,  like  mercury  and  copper,  forms  two  series  of  com- 
pounds which  differ  markedly  from  each  other.  These  are 
the  ferrous  and  ferric  compounds.  Thus  with  chlorine  it 
forms  two  chlorides,  one  of  which,  ferrous  chloride,  has  the 
composition  expressed  by  the  formula  FeCla;  the  other, 
ferric  chloride,  by  FeCl3,  It  appears  from  a  study  of  the 
specific  gravities  of  the  vapors  of  these  chlorides  that  the 
above  formulas  should  be  doubled,  so  that  ferrous  chloride 
is  now  commonly  represented  by  Fe,Cl4,  and  ferric  chloride 
by  Fe2Cl6. 

Similarly  there  are  two  oxides,  FeO  and  Fea03 ;  two  sul- 
phates, ferrous  sulphate,  FeS04,  and  ferric  sulphate, 
Fe,  (S04)3,  etc. 

Ferrous  compounds  show  a  tendency  to  pass  into  ferric 
compounds  by  simple  contact  with  the  air;  and  are  readily 
converted  by  oxidizing  agents,  such  as  nitric  acid,  potassium 
chlorate,  etc.  When,  for  example,  ferrous  hydroxide, 
Fe(OH)2,*  is  exposed  to  the  air  suspended  in  water,  it 
changes  to  ferric  hydroxide,  Fe(OH)8.  The  change  is  repre- 
sented by  the  equation 

2Fe(OH)2  +  H30  +  0  =  2Fe(OH)9. 

*  If  ferrous  chloride  has  the  formula  Fe3Cl4,  it  seems  probable 
that  the  formula  of  ferrous  hydroxide  is  Fea(OH)4.  We  have  DO 
evidence  in  regard  to  this,  and  hence  the  simpler  formula  may  be  used 
here,  particularly  as  we  are  for  the  present  interested  mainly  in  the 
composition  of  the  compound. 
23 


354  INTRODUCTION  TO  CHEMISTRY. 

So,  also,  when  ferrous  chloride  is  left  standing  in  hydro- 
chloric acid  solution  it  changes  to  ferric  chloride,  and  the 
change  is  rapidly  effected  by  boiling  with  a  little  nitric  acid: 

SFeCl,  +  2HC1  +  0  =  aFeCJ.  +  HaO. 


Ferrous  chloride,  FeCl2,  is  formed  by  dissolving  iron  in 
hydrochloric  acid. 

EXPERIMENT  164.—  Dissolve  a  little  iron  wire  in  dilute 
hydrochloric  acid.  Hydrogen  is  evolved,  accompanied  by 
small  quantities  of  other  gases,  whose  formation  is  due  to 
the  presence  of  impurities  in  the  iron,  and  carbon  is  left 
undissolved  as  a  black  residue.  To  a  little  of  the  solution 
in  a  test-tube  add  at  once  caustic  soda.  This  precipitates 
ferrous  hydroxide,  Fe(OH)2,  which  changes  color  rapidly, 
becoming  reddish-brown  finally.  Pure  ferrous  hydroxide 
is  white.  As  it  passes  to  the  ferric  condition  it  becomes 
dirty-green,  and  darker  and  darker  until  it  is  reddish  -brown. 
Heat  another  portion  of  the  solution  of  ferrous  chloride  to 
boiling,  add  two  or  three  drops  of  concentrated  nitric  acid, 
and  boil  again.  Kepeat  this  operation  two  or  three  times. 
The  ferrous  chloride  is  thus  oxidized  to  ferric  chloride.  It 
will  be  noticed  that  the  color  of  the  solution  after  the  oxi- 
dation is  reddish-yellow,  whereas  before  the  oxidation  it 
was  nearly  colorless  or  greenish.  Add  caustic  soda  to  the 
solution  of  ferric  chloride.  A  reddish-brown  precipitate  of 
ferric  hydroxide  will  be  formed.  Just  as  in  this  case  we 
have  passed  from  ferrous  chloride  to  ferric  chloride  by  oxi- 
dation, so  we  can  pass  back  again  to  the  ferrous  compound. 
-7  Thus,  by  adding  a  little  zinc  to  a  solution  of  ferric  chloride 
in  which  hydrochloric  acid  is  present,  the  hydrogen  evolved 


COMPOUNDS  OF  IRON. 


355 


extracts  chlorine  from  the  ferric  chloride  and  converts  it 
into  ferrous  chloride: 

Fe013  +  H  =  FeCla  +  HC1. 

Ferrous  Sulphate,  FeS04  -f  7H20.—  This  salt,  which  is 
commonly  known  as  "green  vitriol"  or  "copperas,"  is 
formed  by  the  action  of  sulphuric  acid  on  iron.  [What  is 
"white  vitriol,"  "blue  vitriol?"]  It  undergoes  change 
in  the  air,  being  converted  into  a  compound  containing 
ferric  sulphate,  Fe2(S04)3,  and  ferric  hydroxide: 

6FeS04  +  30  +  3H20  =  2Fe2(S04)3  +  2Fe(OH)3. 

Iron  alum,  FeK(S04)2  -j-  12H20,  is  formed  by  bringing 
ferric  sulphate  and  potassium  sulphate  together.  It  re- 
sembles ordinary  alum,  A1K(S04)2  -f-  12H20,  but  differs 
from  it  in  containing  iron  instead  of  aluminium. 

Ferrous  oxide,  FeO,  cannot  be  prepared  in  pure  condi- 
tion on  account  of  its  great  affinity  for  oxygen. 

Ferric  oxide,  Fe203,  occurs  in  nature  in  lustrous  crystals 
as  licematite,  and  in  other  valuable  ores  of  iron.  The  hy- 
droxide corresponding  to  this — viz.,  ferric  hydroxide, 
Fe(OH)3 —  is  analogous  in  composition  and  properties  to 
aluminium  hydroxide.  It  is  a  weak  base,  but,  unlike  alumin- 
ium hydroxide,  it  does  not  form  compounds  with  bases. 
Hence  it  does  not  dissolve  in  caustic  soda  and  caustic  potash. 
[Try  it.  Suppose  a  solution  contains  an  aluminium  salt 
and  a  ferric  salt,  and  caustic  soda  be  added,  what  will  first 
take  place  ?  If  more  be  added  and  the  solution  filtered, 
where  will  the  aluminium  be  found,  and  where  the  iron  ?] 

Ferroso-ferric  oxide,  Fe304,  or  magnetic  oxide  of  iron,  is 
found  in  nature  in  the  form  of  loadstone.  It  is  formed 
when  iron  is  burned  in  oxygen  (see  Experiment  25). 


356  INTRODUCTION  TO  CHEMISTRY. 

Ferric  Acid,,  H2Fe04. — It  is  interesting  to  note  that  iron 
combines  with  a  larger  proportion  of  oxygen  than  is  con- 
tained in  any  of  the  compounds  thus  far  mentioned,  and 
then  forms  an  acid.  Potassium  ferrate  has  the  composition 
represented  by  the  formula  K2Fe04. 

The  sulphides  of  iron  have  been  repeatedly  mentioned. 
Ferrous  sulphide,  FeS,  is  made  by  heating  sulphur  and 
iron  together  in  proper  proportions.  It  is  used  in  making 
hydrogen  sulphide  [explain  how]. 

Iron  pyrites,  FeS2,  is  a  yellow  crystallized  substance  very 
abundantly  found  in  nature.  When  heated  in  a  closed 
tube,  sulphur  is  given  off.  When  heated  in  an  open  vessel 
as  upon  a  shallow  iron  pan,  the  sulphur  is  oxidized  to 
sulphur  dioxide,  and  the  iron  is  left  in  the  form  of  the 
oxide.  [Verify  these  statements  by  experiment.] 

Nickel,  Ni  (At.  Wt.  58.5),  is  found  in  meteoric  iron  and 
in  combination  with  arsenic.  It  forms  two  series  of  salts 
corresponding  to  the  two  hydroxides  nickelous  hydroxide, 
Ni(OH)2,  and  nickelic  hydroxide,  Ni(OH)3. 

Most  nickel  salts  are  colored  green. 

Cobalt,  Co  (At.  Wt.  59.1),  is  found  in  combination  with 
arsenic  and  sulphur,  and  also  in  small  quantities  accom- 
panying nickel  in  meteoric  iron. 


CHAPTER  XXIV. 
MANGANESE.— CHROMIUM.— URANIUM.— BISMUTH. 

Manganese,  Mn  (At.  Wt.  55)0— Manganese  is  found  in 
nature  in  the  form  of  oxides,  of  which  manganese  dioxide, 
or  the  black  oxide  of  manganese,  occurs  most  frequently. 
With  oxygen  it  forms  the  following  compounds:  manga- 
nous  oxide,  MnO  ;  manganic  oxide,  Mn,03;  manganoso-man- 
ganic  oxide,  Mn304 ;  manganese  dioxide,  MnOa ;  and  per- 
manganic anhydride,  Mna07. 

Manganese  presents  points  of  resemblance  with  alumin- 
ium and  iron.  Like  iron  it  forms  two  series  of  salts,  the 
manganous  and  manganic  series,  which  differ  from  each 
other  very  much  as  ferrous  and  ferric  salts  do.  Like  iron, 
also,  it  forms  an  oxide,  Mn304,  which  is  analogous  to  the 
magnetic  oxide  of  iron.  Unlike  iron,  it  forms  the  dioxide 
Mn02.  Like  iron,  it  forms  salts,  which  are  derived  from 
an  acid  of  the  formula  H2Mn04 ;  as,  for  example,  potassium 
manganate,  K2Mn04.  Unlike  iron,  it  forms  salts  derived 
from  an  acid  HMn04;  as,  for  example,  potassium  perman- 
ganate, KMn04. 

All  the  higher  oxides  of  manganese  lose  a  part  of  their 
oxygen  very  easily,  and  are  usually  converted  into  mangan- 
ous salts,  like  MnS04,MnC]2,  etc.,  in  which  the  metal  is 
apparently  bivalent.  The  use  of  manganese  dioxide  in 
preparing  oxygen  and  chlorine  has  been  described.  [Give 
an  account  of  the  changes  which  manganese  dioxide  un- 


358  INTRODUCTION  TO  CHEMISTRY. 

dergoes  when  treated  with   sulphuric  acid ;  hydrochloric 
acid;  when  heated.] 

Potassium  Permanganate,  KMn04. — This  salt  is  obtained 
from  potassium  manganate,  K2Mn04,  by  boiling  or  by 
passing  carbon  dioxide  into  it.  The  manganate  is  .made 
by  treating  manganese  dioxide  with  potassium  hydroxide 
and  potassium  chlorate;  in  other  words,  by  oxidizing  man- 
ganese dioxide  in  the  presence  of  the  base,  potassium  hy- 
droxide. The  reaction  is  represented  by  the  equation 

3Mn02  +  6KOH  +  KC103  =  3K2Mn04  +  KOI  +  3H20. 

The  permanganate  is  a  dark-colored,  crystallized  com- 
pound which  dissolves  in  water,  forming  a  deep-purplish 
red-colored  solution. 

EXPERIMENT  165. — In  a  small  porcelain  crucible  heat 
together  5  grams  manganese  dioxide,  Mn02,  5  grams 
solid  potassium  hydroxide,  and  2£  grams  potassium  chlo- 
rate, KC103.  When  the  mass  has  turned  green,  dissolve 
the  contents  in  water  and  boil  the  solution.  The  green 
substance  is  potassium  manganate.  The  color  will  change 
from  green  to  purple. 

Potassium  permanganate  gives  up  its  oxygen  very  readily 
and  changes  to  a  lower  hydroxide.  If  an  acid  is  present 
the  hydroxide  dissolves,  forming  a  colorless  solution. 
When,  therefore,  a  solution  of  potassium  permanganate  is 
added  to  an  acid  solution  containing  an  oxidizable  sub- 
stance it  becomes  colorless. 

EXPEEIMENT  166.— To  a  dilute  solution  of  ferrous  sul- 
phate containing  free  sulphuric  acid  add  drop  by  drop  a 
dilute  solution  of  potassium  permanganate.  The  color 
will  disappear  as  long  as  there  is  any  unchanged  ferrous 
sulphate  present. 


CHROMIUM.  359 

Add  some  permanganate  solution  to  a  solution  of  sul- 
phur dioxide  in  water.  [What  would  you  expect  to  take 
place  in  this  case  ?] 

Add  some  comparatively  dilute  hydrochloric  acid  to  a 
few  crystals  of  potassium  permanganate  in  a  test-tube. 
[Wh'at  do  you  notice  ?  How  do  you  explain  the  change  ?] 

Potassium  permanganate,  KMn04,  is  analogous  to  potas- 
sium perchlorate,  KC104,  not  only  in  composition,  but  in 
its  general  properties. 

Chromium,  and  the  rare  elements  molybdenum,  tung- 
sten, and  uranium  resemble  one  another  sufficiently  to  jus- 
tify us  in  grouping  them  together.  For  the  present  we 
may  confine  our  attention  to  chromium  and  uranium. 

Chromium,  Cr  (At.  Wt.  52.3).— This  element  is  compar- 
atively rare,  and  occurs  almost  only  in  combination  with 
oxygen  and  iron  as  chrpjnixi^irpn.  This  mineral,  whose 
composition  is  represented  by  the  formula  FeCr204,  may 
be  regarded  as  the  iron  salt  of  an  acid  of  the  formula 
HCr02.  Eeplacing  two  atoms  of  hydrogen  of  this  acid  by 
one  of  iron,  we  would  have  a  compound  Fe(Cr02)2.  This 
is  analogous  to  spinel,  which  in  a  similar  way  is  regarded 
as  a  magnesium  aluminate  of  the  formula  Mg(A102)2.  The 
principal  compounds  of  chromium  with  which  we  have  to 
deal  are  potassium  chromate,  K2Cr04;  potassium  dichromate, 
K2Cr207,  and  other  salts  derived  from  chromic  acid. 
There  are,  however,  salts  in  which  chromium  takes  the 
part  of  a  metal,  replacing  the  hydrogen  of  acids;  as,  for  ex^ 
ample,  chromium  sulphate,  Cr2(S04)3. 

Potassium  chromate,  K2Cr04,  is  formed  when  finely 
powdered  chromic  iron  is  heated  with  potassium  carbonate 
and  potassium  nitrate. 

EXPERIMENT   167.  —  Powder  some  chromic  iron  very 


360  INTRODUCTION  TO   CHEMISTRY. 

finely.  Mix  3  grams  with  3  grams  each  of  potassium  car- 
bonate and  potassium  nitrate.  Heat  to  fusion  for  some  time 
in  a  porcelain  crucible.  After  cooling  treat  the  mass  with 
water,  when  a  yellow-colored  solution  will  be  formed.  Po- 
tassium chromate,  K2Cr04,  is  in  the  solution.  Save  this 
solution. 

Potassium  Bichromate,  K2Cr207.  —  This  is  the  form  in 
which  chromium  is  most  frequently  met  with.  It  is 
formed  from  the  chromate  by  adding  acetic  or  nitric  acid. 
The  change  which  takes  place  is  represented  thus  : 


2KaCr04  +  2HN03  •=  2KNOS  +  K2Cr207  +  H20. 

The  relation  between  the  chromate  and  the  dichromate 
will  be  more  readily  understood  by  considering  the  acids 
from  which  they  are  derived.  These  are  chromic  acid, 
H2Cr04,  and  dichromic  acid,  H2O207.  The  latter  may  be 
regarded  as  derived  from  the  former  by  loss  of  water: 


The  same  relation  exists  between  sulphuric  acid,  H2S04, 
and  disulphuric  or  fuming  sulphuric  acid,  H2S207. 

EXPERIMENT  168.  —  To  the  solution  of  potassium  chro- 
mate already  obtained  add  nitric  acid  enough  to  decompose 
the  unused  potassium  carbonate  and  give  the  solution  an 
acid  reaction.  The  color  will  change  from  yellow  to  red. 
The  red  color  .indicates  the  presence  of  the  dichromate. 

When  a  solution  of  potassium  dichromate  is  treated 
with  potassium  hydroxide  until  the  color  becomes  pure 
yellow,  the  chromate  is  formed: 

KaCr,07  +  2KOH  =  2K,Cr04  +  H.O. 


COMPOUNDS  OF  CHROMIUM.  361 

EXPERIMENT  169.— Convert  10  to  20  grams  potassium  di- 
cbromate  into  the  chromate  by  the  method  mentioned. 
Evaporate  to'  crystallization. 

Potassium  dichromate  forms  large  red  crystals,  which 
are  soluble  in  water. 

Both  the  chromate  and  the  dichromate  are  good  oxidiz- 
ing agents. 

EXPERIMENT  170. — Treat  a  little  of  each  salt  in  a  test- 
tube  with  hydrochloric  acid.  [What  evidence  do  you  get 
that  the  salts  are  good  oxidizing  agents  ?] 

The  chromates,  like  the  sulphates  of  barium  and  lead,  are 
insoluble  in  water.  They  are  yellow.  The  lead  salt  is  the 
well-known  pigment  chrome-yellow. 

EXPERIMENT  171. — Add  a  little  of  a  solution  of  potas- 
sium chromate  or  dichromate  to  a  solution  of  a  barium 
salt,  and  of  a  lead  salt. 

Chrome  alum  is  a  salt  allied  to  ordinary  alum,  but  con- 
taining chromium  instead  of  aluminium.  Its  formula  is 
CrK(S04)2  -|-  12H20.  The  alums  have  analogous  formulas: 

Ordinary  alum A1K(S04)2  -f  12H20; 

Iron  alum FeK(S04)2  +  12H20; 

Chrome  alum CrK(SOJ2  +  12H20. 

In  its  general  chemical  conduct  chromium  is  similar  to 
aluminium  and  iron  on  the  one  hand;  while,  on  the  other 
hand,  its  resemblance  to  sulphur  is  unmistakable,  as  is 
seen  in  the  formation  of  the  acids,  chromic  and  dichromic 
acids,  which  are  analogous  to  sulphuric  and  disulphuric 
acids,  not  only  in  composition,  but  in  some  of  their  proper- 
ties. [Are  the  lead  and  barium  salts  of  sulphuric  acid 
soluble  or  insoluble  in  water  ?] 

In  its  conduct  towards  reagents  chromium  more  closely 


862  INTRODUCTION  TO  CHEMISTRY. 

resembles  aluminium  than  iron.  It  forms  no  sulphide  and 
no  carbonate,  so  that  when  a  soluble  carbonate  or  sulphide  is 
added  to  a  solution  of  a  chromium  salt,  such  as  chrome  alum, 
the  hydroxide  is  precipitated,  as  in  the  case  of  aluminium. 
The  hydroxide  dissolves  in  caustic  soda  and  caustic  potash, 
but  is  reprecipitated  when  the  solution  is  boiled.  [How  do 
aluminium  and  iron  hydroxides  act  towards  caustic  soda  ?] 
EXPERIMENT  172.  —  To  a  solution  of  potassium  chromate 
add  some  hydrochloric  acid  and  a  little  alcohol.  On  boil- 
ing the  alcohol  takes  up  oxygen  from  the  chromate,  a  pecu- 
liar smelling  substance,  aldehyde,  is  given  off,  and  the  solu- 
tion now  contains  chromium  chloride,  Cr013.  The  solution 
has  a  green  color.  The  change  is  represented  thus: 

2K,Cr04  +  3C2H60  +  10HC1 

Alcohol. 

=  4KC1  +  2OC13  +  3C2H40  +  8H.O. 

Aldehyde. 

To  separate  portions  of  the  diluted  solution  add  ammo- 
nium sulphide,  sodium  carbonate,  and  sodium  hydroxide. 
The  reactions  which  take  place  are: 


3(NH4)2S  +  6H20 

=  2Cr(OH),  +  6NH.C1  +  3H2S. 

20rCl3  +  3NaaCO,  +  3H20  =  2Cr(OH),  +  6NaCl  +  3C02. 
OrCl,  +  3NaOH  =  Cr(OH)3  +  3Na01. 

After  noticing  the  general  appearance  of  the  precipitate 
formed  with  caustic  soda,  add  an  excess  of  the  latter.  [Does 
the  precipitate  dissolve  ?  How  is  this  explained  ?]  Boil 
the  solution.  [What  takes  place  ?  How  is  this  explained  ?] 

Uranium,  TJ  (At.  Wt.  239).  —  This  element  occurs  mostly 
in  the  form  of  the  oxide  U304  known  as  pitchblende.  It 


BISMUTH  COMPOUNDS.  363 

forms  salts  in  which  the  group  UO,  called  uranyl,  takes  the 
place  of  one  atom  of  hydrogen;  as,  for  example,  uranyl 
nitrate,  (UO)N03  +  3H20;  uranyl  sulphate,  (UO)2S04 
+  3H20. 

Uranium  oxide,  U203,  conducts  itself  towards  bases  like 
an  acid,  forming  salts  called  uranates. 

Just  as  manganese  is  in  some  respects  analogous  to  the 
members  of  the  chlorine  family  [in  what  respects  ?],  and 
chromium  in  some  respects  resembles  the  members  of  the 
sulphur  family  [in  what  respects?],  so  there  is  an  element 
which,  although  usually  acting  the  part  of  a  metal,  is  in 
some  respects  similar  to  the  members  of  the  nitrogen  fam- 
ily. This  is  bismuth. 

Bismuth,  Bi  (At.  Wt.  208),  occurs  mostly  native,  and  is 
obtained  by  heating  the  ores  and  allowing  the  molten  bis- 
muth to  run  out.  In  appearance  it  closely  resembles  anti- 
mony. 

The  chief  compound  of  bismuth  and  oxygen  is  the  yellow 
oxide  Bi203.  This  is  formed  when  bismuth  is  burned  in 
the  air.  If  burned  on  charcoal  a  yellow  film  is  formed. 

EXPERIMENT  173.— Heat  a  small  piece  of  bismuth  on 
charcoal,  and  notice  the  yellow  film.  [What  other  metal 
which  we  have  studied  forms  a  yellow  film  ?  What  differ- 
ence is  there  between  it  and  the  film  caused  by  bismuth  ?] 

The  principal  salt  of  bismuth  is  the  nitrate  Bi(N03), 
+  6H.O. 

Bismuth  sulphide,  Bi2S3  occurs  in  nature,  and  is  formed 
by  passing  hydrogen  sulphide  through  a  solution  of  a  bis- 
muth salt.  It  is  a  black  substance. 

Bismuth  forms  two  classes  of  salts  which  are  known  as 
the  bismuth  and  Usmuthyl  salts.  In  the  former  bismuth 
acts  as  a  trivalent  metal,  taking  the  part  of  three  atoms  of 


364  INTRODUCTION  TO  CHEMISTRY. 

hydrogen,  as  in  the  nitrate,  Bi(N03)3;  in  the  latter,  the 
group  bismuthyl,  BiO,  takes  the  place  of  one  atom  of 
hydrogen,  as  in  bismuthyl  nitrate,  BiO(N08).  Antimony 
forms  similar  salts. 

[What  takes  place  when  sodium  hydroxide  is  added  to  a 
solution  of  a  calcium  salt  ?  a  barium  salt  ?  a  magnesium 
salt  ?  a  zinc  salt  ?  an  aluminium  salt  ?  a  ferrous  salt  ?  a 
ferric  salt  ?  a  chromium  salt  ?  a  copper  salt  ?  What  takes 
place  when  sodium  carbonate  is  added  to  each  of  these 
salts  ?  when  sulphuric  acid  is  added  ?  when  hydrogen  sul- 
phide is  passed  through  the  solutions  ?] 


CHAPTER  XXV. 
THE  LEAD  FAMILY:  LEAD,  TIN.— PLATINUM,  GOLD. 

THE  only  two  members  of  this  family  which  we  need  con- 
sicler  here  are  lead  and  tin.  It  must  be  confessed  that  the 
resemblance  between  these  elements  is  not  very  striking, 
though  there  are  some  points  of  resemblance. 

Lead,  Pb  (At.  Wt.  207). — Lead  occurs  in  combination 

*  x 

in  several  forms  in  nature,  as,  for  example,  in  the  sulphate, 
carbonate,  chromate,  and  sulphide.  The  sulphide,  PbS, 
known  as  galenite,  is  the  most  important  source  of  lead. 
The  extraction  of  the  metal  from  the  sulphide  is  accom- 
plished in  one  of  two  ways: 

(1)  By  heating  the  sulphide  with  iron,  when  the  latter 
combines  with  the  sulphur,  forming  iron  sulphide,  while 
the  lead  is  set  free. 

(2)  By  roasting  the  sulphide  until  it  is  partly  converted 
into  lead  oxide  and  lead  sulphate. 

The  mixture  is  now  heated  without  access  of  air,  when 
the  two  reactions  take  place  which  are  represented  in  these 
equations: 

PbS  +  2PbO  =  3Pb  +  SO,; 

PbS  +  PbS04  =  2Pb  +  2SOf. 

The  lead  is  thus  set  free,  and  the  sulphur  is  driven  off 
as  sulphur  dioxide. 

Lead  is  a  bluish-gray  metal  with  a  high  lustre.     It  is 


366  INTRODUCTION  TO  CHEMISTRY. 

very  soft  and  not  very  strong.  It  melts  at  about  325°. 
All  lead  compounds  are  poisonous.  Nitric  acid  dissolves  it, 
but  hydrochloric  and  dilut6  sulphuric  acids  do  not.  It  is 
precipitated  in  metallic  form  from  a  solution  of  one  of  its 
salts  by  metallic  zinc.  The  formation  is  sometimes  called 
the  "lead  tree"  or  "Arbor  Saturni." 

EXPERIMENT  174. — Dissolve  5  grams  lead  nitrate*  in 
a  litre  of  water,- and  put  the  solution  in  a  bottle.  Suspend 
a  piece  of  granulated  zinc  in  the  centre  of  the  solution,  and 
let  it  stand.  The  lead  will  be  deposited  slowly  in  crystal- 
line form.  At  the  same  time  the  zinc  will  pass  into  solu- 
tion. The  zinc  simply  replaces  the  lead: 

Zn  +  Pb(N03)a  =  Zn(NO3)a  +  Pb. 

After  the  tree  has  formed,  filter  off  some  of  the  solu- 
tion and  see  whether  zinc  is  contained  in  it  or  not.  There 
will  probably  be  some  lead  left,  so  that  in  order  to  detect 
the  zinc  the  lead  will  have  to  be  removed  first  This  may 
be  done  by  adding  sulphuric  acid  and  alcohol.  The  sul- 
phate of  lead  is  thus  formed.  As  this  is  somewhat  soluble 
in  water  and  insoluble  in  alcohol,  the  latter  is  added.  Filter 
off  the  lead  sulphate,  and  to  the  filtrate  add  just  enough 
ammonia  to  neutralize  the  sulphuric  acid,  and  then  ammo- 
nium sulphide.  White  zinc  sulphide  is  precipitated. 

If  all  the  lead  is  not  precipitated  by  the  sulphuric  acid, 
the  precipitate  caused  by  ammonium  sulphide  will  not  be 
white,  but  more  or  less  inclined  towards  black,  according  to 
the  quantity  of  lead  sulphide  present  All  the  lead  may 
be  precipitated  in  the  first  instance  by  first  adding  some 
hydrochloric  acid  [What  effect  will  this  have  on  the  solution 

*  Instead  of  lead  nitrate,  the  acetate  or  sugar  of  lead  may  be  used. 


COMPO  UNDS  OF  LEAD.  367 

of  the  lead  salt?  Which  chlorides  are  insoluble?]  and  then 
passing  hydrogen  sulphide  through  the  solution.  Filter 
off  and  add  ammonia  and  ammonium  sulphide  to  the 
filtrate. 

Lead  forms  three  distinct  compounds  with  oxygen,  viz. : 
lead  suboxide,  Pb,0;  lead  oxide,  PbO;  .and  lead  peroxide, 
Pb02.  Red-lead,  or  minium,  is  apparently  a  mixture  of 
the  oxide  and  peroxide,  and  has  approximately  the  compo- 
sition Pb304. 

Lead  oxide,  PbO,  is  known  by  the  name  of  litharge.  It 
is  formed  by  the  oxidation  of  molten  lead  in  contact  with 
the  air.  When  litharge  is  heated  in  the  air  to  400°  it  takes 
up  oxygen  and  is  converted  into  the  mixture  of  oxides  known 
as  minium,  or  red-lead,  Pb304(  =  2PbO  -f  Pb02).  When 
heated  to  a  high  temperature  it  gives  up  oxygen  and  is 
again  converted  into  yellow  lead  oxide.  Treated  with  nitric 
acid,  a  part  is  dissolved  forming  lead  nitrate,  while  lead 
peroxide,  a  brown  powder,  remains  behind. 

EXPERIMENT  175. — Treat  a  little  minium  with  ordinary 
dilate  nitric  acid,  and  note  .the  change  in  color.  [Does  lead 
pass  into  solution?  How  do  you  know?] 

Lead  peroxide,  Pb02,  conducts  itself  somewhat  like  man- 
ganese dioxide.  When  treated  with  hydrochloric  acid 
chlorine  is  evolved: 

Pb02  +  4HC1  =  PbCl2  +  2H20  +  Ols. 

EXPERIMENT  176.— Treat  a  little  lead  peroxide  with  hy- 
drochloric acid  in  a  test-tube.  [In  what  form  is  the  lead 
after  the  experiment?  Is  the  product  soluble  or  insoluble 
in  water?] 

Heated  with  sulphuric  acid,  oxygen  is  given  off  and  lead 
sulphate  is  formed. 


368  INTRODUCTION  TO   CHEMISTRY. 

EXPERIMENT  177. — Heat  some  lead  oxide  with  sulphuric 
acid.  Show  that  oxygen  is  given  off.  [What  is  left  be- 
hind? Is  it  soluble  or  insoluble?] 

Among  the  more  important  salts  of  lead  are  the  sulphate, 
PbS04;  the  nitrate,  Pb(N03)2;  the  carbonate,  PbC03;  the 
acetate,  Pb(02H302)2;  the  chromate,  PbC04;  and  the  sul- 
phide, PbS.  The  acetate  and  nitrate  are  soluble  in  water; 
the  others  are  not. 

Lead  acetate,  Pb(C2H302)2,  commonly  called  "sugar  of 
lead/'  is  the  lead  salt  of  acetic  acid,  C2H402,  which  is  the 
acid  contained  in  vinegar.  It  is  formed  by  dissolving  lith- 
arge in  acetic  acid. 

The  sulphate,  chromate,  and  chloride  have  already  been 
referred  to.  They  are  formed  by  adding  a  soluble  sulphate, 
chromate,  and  chloride  to  a  solution  of  a  lead  salt.  The 
chromate  is  the  well-known  chrome  yelloiv.  Lead  chloride 
is  soluble  in  hot  water,  but  only  slightly  soluble  in  cold 
water.  It  crystallizes  from  its  solution  in  hot  water. 

EXPERIMENT  178.— To  a  dilute  solution  of  lead  nitrate 
or  acetate  add  some  hydrochloric  acid.  Heat  and  thus  dis- 
solve the  precipitate,  and  stand  it  aside.  On  cooling,  the 
lead  chloride  will  crystallize  out.  It  is  not  soluble  in  am- 
monia. [Does  it  differ  from  silver  chloride  in  this  respect?] 

Lead  carbonate,  PbC03,  is  the  well-known  and  much- 
used  pigment  called  white-lead. 

Lead  sulphide,  PbS,  is  the  important  mineral  galenite  to 
which  reference  has  been  made.  The  com  pound  is  precipi- 
tated by  passing  hydrogen  sulphide  through  a  solution  of  a 
lead  salt,  or  by  adding  a  soluble  sulphide  to  such  a  solution. 

[How  can  you  distinguish  between  a  lead  and  a  barium 
salt  without  using  hydrogen  sulphide?  Between  lead  and 


COMPOUNDS  OF  TIN.  369 

silver  without  using  hydrogen  sulphide  or  hydrochloric 
acid?  By  hydrochloric  acid  alone  ?]t 

Tin,  Sn  (At  Wt.  118), — Tin  occurs  in  nature  mostly  as  tin 
stone,  which  is  the  oxide  Sn09.  The  metal  is  obtained 
from  the  ore  by  reducing  with  charcoal.  It  is  a  white 
metal,  which  in  general  appearance  resembles  silver.  It  is 
soft  and  malleable,  and  can  be  hammered  out  into  very 
thin  sheets,  forming  thus  the  well-known  tin-foil.  At  200° 
it  is  brittle.  .  It  melts  at  228°.  It  remains  unchanged  in 
the  air  at  ordinary  temperatures.  It  dissolves  in  hydro- 
chloric acid,  forming  stannous  chloride,  SnCl2;  in  sulphuric 
acid,  forming  stannous  sulphate,  SnS04,  sulphur  dioxide 
being  evolved  at  the  same  time  [explain  this].  Ordinary 
concentrated  nitric  acid  oxidizes  it,  the  product  being  a 
compound  of  tin,  oxygen,  and  hydrogen,  known  as  meta- 
stannic  acid,  which  is  a  white  powder  insoluble  in  nitric 
acid  and  in  water. 

Tin  forms  two  classes  of  compounds,  the  stannous  and 
'stannic  compounds.  These  do  not  bear  to  each  other  the 
same  relation  as  that  which  exists  between  cuprous  and 
cupric  .compounds  [what  is  this?],  or  that  between  ferrous 
and  ferric  compounds  [what is  this?].  In  stannous  com- 
pounds the  tin  appears  to  be  bivalent,  as  indicated  by 
the  formulas  SnCl2,  SnO,  SnS,  which  respectively  repre- 
sent stannous  chloride,  oxide,  and  sulphide.  In  stannic 
compounds,  on  the  other  hand,  the  tin  appears  to  be  quad- 
rivalent, as  indicated  by  the  formulas  SnCl4,  Sn02,  SnS2, 
which  respectively  represent  stannic  chloride,  oxide,  and 
sulphide. 

In  general,  stannous  compounds  are  readily  converted 
into  stannic  compounds. 

Stannous  chloride,  SnCl2,  is  formed  by  dissolving  tin  in 
24 


370  INTRODUCTION  TO   CHEMISTRY. 

hydrochloric  acid.  If  a  solution  of  stannous  chloride  be 
added  to  a  solution  of  mercuric  chloride,  or  corrosive  subli- 
mate, the  latter  is  reduced  to  mercurous  chloride,  and  this, 
being  insoluble  in  water,  appears  us  a  precipitate.  When 
stannous  chloride  and  mercuric  chloride  are  heated  together 
in  solution,  metallic  mercury  is  formed: 


2HgCl2  +  SnCl2  =  2HgCl  +  SnCl 


4 


EXPERIMENT  179.  —  Dissolve  a  few  grams  of  tin  in  ordi- 
nary dilute  hydrochloric  acid.  Add  a  little  of  this  solu- 
tion to  a  solution  of  mercuric  chloride.  A  white  precipi- 
tate of  mercurous  chloride  will  be  formed.  Heat  the  two 
solutions  together,  and  notice  the  formation  of  metallic 
mercury,  which  appears  as  a  gray  powder. 

Stannic  oxide,  Sn02,  occurs  in  nature  as  tin  stone.  It  is 
obtained  by  burning  tin  in  the  air.  When  melted  together 
with  caustic  soda  it  dissolves  as  sodium  stannate.  This  ac- 
tion suggests  that  which  takes  place  when  silicon  dioxide 
is  melted  with  an  alkali  and  a  silicate  is  formed,  and  when 
carbon  dioxide  and  an  alkali  are  brought  together.  The 
formulas  of  the  products  in  these  cases  are  similar,  viz.: 
Na2Sn03,  Na2Si08,  and  Na.OO,. 

Metastannic  acid,  Sn04H4,  is  formed  by  oxidizing  tin  with 
ordinary  concentrated  nitric  acid.  At  100°  it  is  converted 
into  stannic  acid,  H2Sn03,  and  at  red  heat  into  stannic 
oxide,  SnOa: 

H4Sn04  =  H.SnO,  +  HaO; 
H2Sn03  =  Sn02  -f  HaO. 

[Are  there  any  analogous  facts  known  in  connection  with 
silicon?  Compare  the  oxides  and  acids  of  carbon,  silicon, 


COMPOUNDS  OF  TIN.  371 

and  tin,  not  only  as  regards  their  formulas,  but  as  regards 
their  properties  and  transformations.] 

Stannic  chloride,  SnCl4,  is  made  by  heating  tin  in  chlo- 
rine. It  is  a  heavy  liquid,  which  distils  at  120°  without 
suffering  decomposition.  It  fumes  in  the  air  very  strongly. 
It  has  a  marked  affinity  for  water,  and  is  used  as  a  dehy- 
drating agent  in  a  number  of  reactions.  In  solution  it  is 
obtained  by  dissolving  tin  in  aqua  regia.  In  this  case  the 
stannous  chloride  formed  by'the  action  of  the  hydrochloric 
acid  on  the  tin  is  oxidized  by  the  nitric  acid: 

Sn012  +  2HC1  +  0  =  SnCl4  +  H20. 

[What  happens  when  a  solution  containing  ferrous  chlo- 
ride is  treated  with  nitric  acid?] 

Stannic  sulphide,  SnS2,  is  a  yellow  substance  looking  like 
arsenic  sulphide.  It  is  formed  by  passing  hydrogen  sul- 
phide through  a  dilute  solution  of  stannic  chloride.  It  is 
soluble  in  yellow  ammonium  sulphide. 

EXPERIMENT  180.— Dissolve  a  little  tin  in  aqua  regia. 
Make  the  solution  very  dilute,  and  pass  hydrogen  sulphide 
through  it.  Filter  off,  wash,  and  treat  with  yellow  ammo- 
nium sulphide.  [Does  the  precipitate  dissolve?  Add  an 
acid  to  the  solution.  What  takes  place?] 

Tin  is  used  very  extensively  in  the  manufacture  of  uten- 
sils of  various  sorts,  and  in  preparing  several  valuable 
alloys.  Among  these  are  solder,  which  consists  of  tin 
and  lead;  britannia,  which  consists  of  9  parts  of  tin  and  1 
part  of  antimony;  bronze,  which  consists  of  tin  and  cop- 
per. 

A  peculiarity  of  tin  which  distinguishes  it  from  most 
other  metals  is  its  conduct  towards  nitric  acid.  As  already 
stated,  instead  of  dissolving  in  the  acid,  it  is  converted  into 
a  white,  insoluble  compound, — metastannic  acid.  Anti- 


372  INTRODUCTION  TO  ' CHEMISTRY. 

mony  is  also  converted  into  a  white  oxide  by  nitric  acid, 
but  antimony  does  not  dissolve  in  hydrochloric  acid,  while 
tin  does. 

EXPERIMENT  181. — Treat  a  little  tin  with  strong  nitric 
acid,  and  notice  the  formation  of  the  white  metastannic 
acid.  [Is  it  soluble  in  water?]  Treat  a  little  antimony  in 
the  same  way.  Now  treat  each  element  separately  with 
hydrochloric  acid. 

EXPERIMENT  182. — Examine  a  small  piece  of  solder,  and 
show  that  it  contains  lead  and  tin.  Treat  with  aqua  regia; 
dilute  with  water.  [Will  all  the  lead  pass  into  solution 
under  these  circumstances?  Will  any  of  it?]  Pass  hydro- 
gen sulphide  through  the  much-diluted  solution.  Filter 
off  the  precipitate;  wash  with  hot  water;  treat  with  yellow 
ammonium  sulphide;  filter;  add  an  acid  to  the  filtrate. 
[Explain  what  takes  place  in  each  step.]  The  formation 
of  a  yellow  precipitate,  which  is  soluble  in  yellow  ammo- 
nium sulphide,  is  not  conclusive  evidence  that  tin  is 
present,  for  arsenic  sulphide  has  similar  properties.  In 
order  to  distinguish  between  them  advantage  may  be 
taken  of  the  fact  that  arsenic  sulphide  is  soluble  in  a 
solution  of  ammonium  carbonate,  while  stannic  sulphide  is 
not.  Treat  some  of  the  precipitate  with  a  solution  of  am- 
monium carbonate;  filter;  add  an  acid,  when,  if  any  arse- 
nic sulphide  is  in  solution,  it  will  be  precipitated. 

EXPERIMENT  183. — Examine  a  small  piece  of  bronze, 
and  show  that  it  consists  of  tin  and  copper.  In  this  case, 
after  getting  the  two  metals  in  solution,  by  means  of  aqua 
regia,  dilute  and  pass  hydrogen  sulphide  through  until 
the  solution  is  saturated.  Filter;  wash;  treat  with  yellow 
ammonium  sulphide.  Filter;  acidify;  prove  that  the  yellow 
precipitate  is  not  arsenic  sulphide.  Dissolve  the  black  pre- 


PALLADIUM.  —PLATINUM.  373 

cipitate,  which  is  mostly  insoluble  in  ammonium  sulphide, 
in  nitric  acid.  [What  change  will  the  copper  sulphide  un- 
dergo when  treated  with  nitric  acid?]  Treat  a  little  of  the 
solution  with  caustic  soda,  arid  boil.  [What  changes  take 
place?]  Filter  and  wash.  Mix  some  of  the  black  precipi- 
tate with  sodium  carbonate,  and  heat  in  the  reducing  flume 
of  the  blow-pipe.  [What  evidence  do  you  then  get  of  the 
presence  of  copper?] 

Palladium,  ruthenium,  and  rhodium  are  three  rare  ele- 
ments which  closely  resemble  one  another. 

^Palladium  forms  with  hydrogen  a  compound  which  in 
general  has  the  properties  of  alloys.  It  has  the  composi- 
tion Pd2H,  and  contains  about  600  volumes  of  hydrogen  to 
1  volume  of  palladium.  The  properties  of  this  substance 
have  led  to  the  view  that  hydrogen  has  metallic  properties. 
If  by  the  name  metal  is  meant  an  element  which  forms 
salts  with  acids,  then  it  may  be  said  that  hydrogen  bears 
to  other  metals  a  relation  similar  to  that  which  carbonic 
acid  bears  to  other  acids.  Acids  are  simply  salts  of  hydro- 
gen, and  other  metals  drive  out  the  hydrogen.  Carbon- 
ates are  in  the  same  way  decomposed  by  all  other  acids. 

Platinum,  osmium,  iridium,  and  gold  form  a  family  in 
which,  however,  the  three  first  mentioned  are  the  most 
closely  related.  Of  these  three,  platinum  is  the  best 
known. 

Platinum,  Pt  (At.  Wt.  194.8),  occurs  almost  always  ac- 
companied by  iridium,  palladium,  rhodium,  ruthenium, 
and  osmium,  in  the  form  of  alloys.  The  ore  is  found  in 
the  Ural  Mountains,  in  California,  Australia,  and  a  few 
other  places.  It  is  prepared  by  treating  the  ore  with 
strong  aqua  regia,  which  dissolves  the  platinum,  together 
with  some  iridium.  The  platinum  chloride  thus  obtained 


374  INTRODUCTION  TO  C&BMISTBY. 

is  precipitated  by  means  of  ammonium  chloride,  witli 
which,  as  with  potassium  chloride  (see  p.  319),  it  forms 
a  difficultly  soluble  compound,  Pt014  +  2NH4C1,  or 
(NH4)2PtCl6.  When  this  is  heated  to  a  sufficiently  high 
temperature  it  is  decomposed,  leaving  metallic  platinum 
as  a  residue.  By  special  methods  the  indium  can  be  sepa- 
rated from  it. 

Platinum  is  a  grayish-white  metal,  with  a  high  lustre. 
Its  specific  gravity  is  21.15,  it  being  one  of  the  heaviest 
substances  known.  The  specific  gravity  of  iron  is  7.8, 
that  of  lead  11.4,  and  that  of  lithium  0.59.  In  other  words, 
a  piece  of  platinum  weighs  nearly  three  times  as  much  as 
a  piece  of  iron  of  the  same  dimensions,  and  nearly  twice 
as  much  a§  a  piece  of  lead  of  the  same  dimensions. 
Platinum  is  not  dissolved  by  hydrochloric,  nitric,  or  sul- 
phuric acid;  but  aqua  regia  dissolves  it,  forming  platinum 
chloride,  PtCl4.  Fusing  caustic  alkalies  attack  it;  sodium 
carbonate  does  not.  It  does  not  change  in  the  air,  and 
does  not  melt  except  in  the  flame  of  the  oxyhydrogen  blow- 
pipe. It  resists  the  action  of  most  substances.  These 
properties  make  it  extremely  valuable  to  the  chemist. 
Platinum  crucibles  and  evaporating-dishes,  foil,  and  wire 
are  constantly  used  in  the  laboratory,  and  it  is  difficult  to 
see  how  we  could  get  along  without  them.  Large  retorts 
of  platinum  are  used  for  the  purpose  of  concentrating 
sulphuric  acid  arnd  distilling  it. 

Platinum  chloride,  PtCl4,  is  made  by  dissolving  the- metal 
in  aqua  regia  and  evaporating  off  the  acids.  It  dissolves  in 
water,  forming  a  yellowish-red-colored  solution,  which  is 
used  in  the  laboratory  for  the  purpose  of  precipitating  po- 
tassium from  its  solutions,  as  the  salt  potassium  chloro- 
platinate,  K2PtCl6,  or  PtCl4  +  2KC1,  is  difficultly  soluble 


GOLD.  375 

in  water.  The  corresponding  sodium  salt,  Na2PtCl6  -f- 
6H,0,  is  easily  soluble  in  water.  There  is  another  chloride 
of  platinum  of  the  formula  PtCl3,  known  as  platinous 
chloride. 

Platinum  chloride  combines  with  ammonia  in  a  great 
many  different  proportions,  forming  the  so-called  platinum 
bases.  The  discussion  of  these  compounds  would  lead  us 
too  far  at  present. 

Gold,  Au  (At.  Wt  196.7).— Gold  usually  occurs  native. 
It  is  found  enclosed  in  quartz,  or  more  frequently  in  quartz 
sand.  It  is  separated  mechanically  by  washing,  and  then 
extracted  with  mercury,  which  forms  an  amalgam  with  it. 
The  amalgam  is  afterwards  heated,  when  the  mercury 
passes  over  and  the  gold  remains  behind. 

Gold  is  a  yellow  metal  with  a  high  lustre.  It  is  quite 
soft  and  extremely  malleable.  Its  specific  gravity  is  19.3. 

It  combines  directly  with  chlorine,  but  not  with  oxygen. 
The  three  acids  hydrochloric,  nitric,  and  sulphuric  "acid  do 
not  act  upon  it;  but  aqua  regia  dissolves  it,  forming  gold 
chloride.  From  its  solutions  it  is  thrown  down  in  uncom- 
bined  condition  by  various  reducing  agents,  as,  for  exam- 
ple, ferrous  sulphate,  FeS04 : 

3FeS04  +  AuCl3  =  Fe2(S04)3  +  FeCl3  +  Au. 

Goldware  and  coin  are  made  of  an  alloy  of  gold  and  cop- 
per. The  standard  gold  coin  of  the  United  States  contains 
nine  parts  of  gold  to  one  of  copper.  The  composition  of 
gold  used  for  jewelry  is  usually  stated  in  terms  of  carats. 
Pure  gold  is  24-carat  gold  ;  20-carat  gold  contains  20  parts 
gold  and  4  parts  copper ;  18-carat  gold  contains  18  parts 
gold  and  6  parts  copper,  etc. 


CHAPTER  XXVI. 

GENERAL    CONSIDERATIONS.— NATURAL    GROUPS    OF 
ELEMENTS.— CONCLUSION. 

WE  have  now  studied  a  number  of  the  chemical  elements 
and  the  way  they  act  upon  one  another.  We  have  also 
made  the  acquaintance  of  a  goodly  number  of  chemical 
compounds,  and  have  studied  to  some  extent  their  action 
upon  one  another.  We  have  learned  that  there  are  certain 
characteristics  which  distinguish  chemical  action  from  all 
other  kinds  of  action;  and  that  there  are  laws  governing 
all  cases  of  chemical  action,  as  there  are  laws  governing  the 
motions  of  the  heavenly  bodies.  These  laws  were  discov- 
ered by  careful  study  of  a  large  number  of  cases.  When 
it  was  found  that  they  hold  true  in  the  cases  studied,  it 
was  assumed  that  they  hold  true  in  all  cases.  The  law  is 
only  a  statement  of  what  is  found  to  be  true  so  far  as  ex- 
amination has  extended.  The  two  fundamental  laws  of 
chemical  action  are  the  laws  of  definite  and  multiple  pro- 
portions, but  a  great  many  more  laws  must  be  discovered 
before  we  can  form  any  conception  in  regard  to  the  real 
cause  of  chemical  action.  The  facts  which  we  have  become 
acquainted  with  thus  far  show  that  the  chemical  elements 
differ  from  one  another  very  markedly.  Some,  like  chlo- 
rine, phosphorus,  potassium,  are  extremely  active;  while 
others,  like  nitrogen,  are  inert.  Some  chemical  reactions 
take  place  violently,  others  with  scarcely  a  perceptible  evo- 


GENERAL   CONSIDERATIONS.  377 

lution  of  heat.  Why  these  differences?  Why  aoes  chlo- 
rine attack  and  combine  with  nearly  every  other  element, 
while  gold  can  scarcely  be  made  to  unite  with  other  ele- 
ments? Why  does  chlorine  combine  with  hydrogen,  vol- 
ume for  volume,  while  oxygen  combines  with  the  same 
element  in  the  proportion  of  one  volume  to  two;  and  nitro- 
gen in  the  proportion  of  one  to  three,  etc.  ?  What  are  the 
differences  which  we  recognize  under  the  name  of  valence 
due  to?  Why  do  some  elements  resemble  one  another 
closely,  so  that  a  relationship  is  recognized  at  once?  Is 
there  any  connection  between  the  families  of  the  elements? 
Why  are  some  substances  acids  and  some  bases?  What  is 
the  real  difference  between  acids  and  bases?  Why  can 
chlorine  and  nitrogen  combine  with  oxygen  in  so  many 
different  proportions,  while  potassium,  calcium,  and  other 
elements  combine  with  oxygen  in  only  -one  proportion? 
These  are  some  of  the  questions  which  will  suggest  them- 
selves to  the  student.  But  the  questions  cannot  be 
answered  at  present.  The  answers  can  only  be  given  by 
long-continued  painstaking  investigation  of  the  facts  of 
chemistry;  or,  in  other  words,  by  the  same  means  that  has 
made  chemistry  what  it  is  to-day.  The  amount  of  work  it 
has  taken  to  establish  the  facts  considered  in  this  work  is 
enormous.  It  began  .away  back  in  the  dark  ages,  and  has 
continued  with  increasing  energy  to  the  present.  The 
science  of  chemistry  is  the  result  of  this  work.  Nothing 
mysterious  has  been  involved  in  the  growth.  There  are 
always  those  who  have  the  desire  to  learn  more  than  is 
known  in  regard  to  the  matters  with  which  they  are  occu- 
pied. If  the  desire  leads  to  actual  work,  undertaken  for 
the  purpose  of  enlarging  knowledge,  something  of  value  is 
sure  to  be  learned.  Most  important  discoveries  have  been 


INTRODUCTION  TO  CHEMISTRY. 

made  as  the  result  of  investigations  in  regard  to  compara- 
tively simple  phenomena.  One  thing  suggests  another, 
until,  by  a  consideration  of  a  number  of  facts,  relations  are 
seen  which  were  not  dreamed  of  before,  and  things  which 
appeared  difficult  become  simple.  The  time  will  come 
when  the  connection  between  the  facts  of  chemistry  will  be 
discerned.  It  will  then  no  longer  be  a  difficult  thing  to 
classify  the  elements.  They  will  be  seen  to  form  a  natural 
series  in  which  each  element  has  its  place,  and  the  proper- 
ties of  the  elements  will  be  seen  to  be  determined  by  the 
place  which  they  occupy  in  the  system.  Indeed,  the  time 
has  already  come  when  it  can  be  shown  that  there  is  a  close 
connection  between  the  atomic  weights  of  the  elements  and 
many  of  their  other  properties.  While  it  is  not  possible  to 
discuss  this  subject  with  any  degree  of  fulness  at  present,  a 
brief  account  will  serve  to  give  an  idea  of  the  character  of 
the  connection. 

Attention  has  repeatedly  been  called  to  the  curious  rela- 
tions existing  between  the  atomic  weights  of  members  of 
the  same  family  of  elements,  as  in  the  case  of  chlorine, 
bromine,  and  iodine;  calcium,  strontium,  and  barium; 
lithium,  sodium,  and  potassium,  and  others.  A  careful 
study  has  shown  that  these  relations  are  more  extensive 
than  appears  at  first  sight.  If,  leaving  out  hydrogen, 
and  beginning  with  lithium,  which  next  to  hydrogen  has 
the  lowest  atomic  weight,  we  arrange  the  elements  in  the 
order  of  their  atomic  weights,  the  first  fourteen  will  ex- 
hibit a  most  remarkable  relation,  as  is  shown  in  the  sub- 
joined table: 

Li  =  7;  Gl  =  9.1;  B  =  11;  0  =  12;  N=14;  O=16;  F=19; 
Na=23;  Mg=24;  Al=27;  Si=28;  P=31;  S=32;  01=35.5. 


MENDELEJEPWS  TABLE.  379 

The  elements  whose  symbols  stand  under  each  other  in 
this  table  have  similar  chemical  properties.  This  is  marked 
in  the  case  of  lithium  and  sodium  ;  carbon  and  silicon  ; 
nitrogen  and  phosphorus  ;  oxygen  and  sulphur  ;  and  fluo- 
rine and  chlorine.  Proceeding  in  the  same  way,  the  ele- 
ment with  the  next  higher  atomic  weight  is  potassium, 
39.1.  This  comes  in  the  same  perpendicular  line  with 
lithium  and  sodium  or  with  members  of  the  same  family, 
Then  follow  calcium,  scandium,  titanium,  vanadium, 
chromium,  and  manganese,  each  of  which  falls  naturally 
in  the  perpendicular  line  which  contains  elements  allied  to 
it.  It  has  been  found  possible  in  this  way  to  arrange  all 
the  elements  in  one  table*  which  exhibits  the  relations  be- 
tween their  atomic  weights  and  properties.  Several  tables 
have  been  proposed,  but  they  do  not  differ  essentially  from 
one  another.  That  suggested  by  the  Russian  chemist 
Mendelejeff  is  here  given.  The  atomic  weights  used  in  the 
table  have  been  calculated  with  care  from  the  results  of  the 
most  trustworthy  determinations  made  by  different  chem- 
ists. In  some  cases  they  will  be  found  to  differ  slightly 
from  those  in  common  use  : 


380 


INTRODUCTION  TO   CHKMISTRT. 


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CONCLUSION.  881 

It  will  be  seen  that  in  Group  I.  are  the  metals  of  the 
alkalies;  in  Group  II.,  calcium,,  strontium,  and  barium, 
magnesium,  zinc,  and  cadmium  ;  in  Group  IV.,  carbon, 
silicon,  tin,  lead  ;  in  Group  V.,  nitrogen,  phosphorus,  vana- 
dium, arsenic,  etc.;  in  Group  VI.,  sulphur,  selenium,  tel- 
lurium, chromium,  molybdenum  ;  in  Group  VII.,  fluorine, 
chlorine,  bromine,  and  iodine,  and  manganese.  Between 
the  fourth  series  ending  with  manganese  and  the  next  one 
beginning  with  copper  there  are  three  similar  elements, 
iron,  cobalt,  and  nickel.  So,  too,  a  similar  group  of  three 
elements — ruthenium,  rhodium,  and  palladium — comes  be- 
tween the  the  sixth  and  seventh  series;  and  another,  con- 
sisting of  osmium,  iridium,  and  platinum,  between  the 
tenth  and  eleventh.  Passing  from  left  to  right  in  each 
series,  we  find  that  the  elements  can  combine  with  a  larger 
and  larger  relative  quantity  of  oxygen.  The  only  oxygen 
compound  of  lithium  has  the  formula  Li30.  The  oxide  of 
glucinum  is  G10;  that  of  boron,  B203 ;  that  of  carbon, 
which  contains  the  largest  proportion  of  oxygen,  is  CO, ; 
that  of  nitrogen,  N204;  that  of  sulphur,  S03  ;  and  that  of 
chlorine,  C1207.  On  the  other  hand,  the  power  to  combine 
with  hydrogen  increases  until  a  limit  is  reached  as  we  pass 
from  right  to  left,  as  is  shown  in  the  compounds  FH,  OH2, 
NH3,  and  OH4. 

Those  elements  which  have  the  strongest  metallic  char- 
acter, whose  hydroxides  are  the  strongest  bases,  are  in- 
cluded in  Group  I.  The  hydroxides  of  the  metals  in  Group 
II.  are  weaker  bases,  those  of  the  elements  in  Group  III. 
are  weaker  still,  while  when  we  reach  Group  IV.  the  hy- 
droxides of  some  of  the  elements  included  in  it  have  weak 
acid  properties  and  no  basic  properties.  The  elements  of 
Group  V.  are  nearly  all  acid-forming.  Those  of  Group 


382  INTRODUCTION  TO   CHEMISTRY. 

VI.  form  strong  acids,  as  do  those  of  Group  VII.  If  we 
know  the  atomic  weight  of  an  element  we  can  say  ap- 
proximately where  it  belongs  in  the  table,  and  can  from  its 
position  determine  its  properties  with  considerable  ac- 
curacy. When  the  table  was  first  constructed,  the  two 
elements  scandium  and  gallium  were  undiscovered.  It 
was  seen,  however,  that  the  gaps  existed,  and  it  was  pre- 
dicted that  elements  would  be  found  with  atomic  weights 
approximately  44  and  69  respectively,  and  that  these  ele- 
ments would  have  certain  properties  which  were  clearly 
described.  It  was  suggested  that  the  element  with  the 
atomic  weight  44  would  bear  to  calcium  and  titanium 
about  the  same  relation  that  aluminium  bears  to  magne- 
sium and  silicon.  The  predictions  were  soon  after  con- 
firmed, and  the  description  of  the  element  given  before  it 
was  discovered  was  found  to  be  singularly  correct.  Un- 
questionably the  properties  of  the  elements  are  determined 
by  their  atomic  weights.  An  element  whose  atom  weighs 
100  times  as  much  as  that  of  hydrogen  must  have  certain 
definite  properties.  It  must  combine  with  hydrogen  and 
with  oxygen  in  certain  proportions ;  it  must  be  allied  to 
the  members  of  the  chlorine  family;  its  properties  are  the 
result  of  that  particular  weight.  Further,  it  seems  to  fol- 
low that  the  elements  are  not  entirely  independent  forms 
of  matter,  but  that  they  are  in  all  probability  compounds 
of  a  small  number  of  simple  elements  at  present  unknown 
to  us.  Of  this,  however,  we  have  no  evidence,  and  until 
some  one  succeeds  in  isolating  one  or  more  of  these  subtler 
elements  it  is  almost  useless  to  speculate  in  regard  to  them. 


INDEX. 


Acetylene,  178,  180 

Acid,  acetic,  178 
arsenic,  273 
arsenious,  273 
boric,  277 
bromic,  239 
carbonic,  189 
chloric,  112 
chlorous,  116 
chromic,  360 
dithionic,  263 
ferric,  357 
formic,  178 
hydriodic,  249 
hydrobromic,  239 
hydrochloric,  63,  102 
hydrocyanic,  205 
hydrofluoric,  243 
hydrosulplmrous,  263 
hypobromous,  239 
hypochlorous,  112 
iodic,  242 
metaboric,  277 
metarsenic,  273 
metaphosphoric,  269 
metastannic,  370 
nitric,  63,  148 
nitrous,  154 
orthophosphoric,  269 
oxalic,  178 
perchloric,  116 
phosphoric,  269 
phosphorous,  270 
pyroarsenic,  273 
pyrophosphoric,  269 
pyrosulplmric,  263 


Acid,  selenic,  263 

silicic,  281 

sulphuric,  63,  259 

fuming,  263 

sulphurous,  258 

tartaric,  178 

telluric,  263 

tetraboric,  278 

tetrathionic,  263 

thiosulphuric,  263 

trithionic,  263 
Acids,  122 

characteristics,  121  \ 

dibasic,  261 

monobasic,  261 

tribtisic,  269 

Acid-forming  elements,  238 
Affinity,  chemical,  27 
Agate,  282 
Air,  127 

analysis,  128 
Alcohol,  ethyl,  178 

methyl,  178 
Aldehydes,  178 
Alkalies,  117 
Alloys,  336 
Allylene,  178 
Alum,  349 
Aluminium,  347 

chloride,  348  . 

hydroxide,  348 

oxide,  348 

silicates,  349 
Alums,  349 
Am  alga  ins,  239 
Amethyst,  282 


384 


INDEX. 


Ammonia,  138 

composition,  143 

formation,  137 

in  air,  134 

in  gas  liquor,  138 
Ammonium,  143 

chloride,  138,  317 

liydrosulphide,  319 

salts,  143,  316 

sulphide,  317 
Analysis,  253 
Anhydride,  156 

boric,  278 

carbonic,  180 

nitric,  156 

nitrous,  156 

silicic,  282 
Antimony,  274 
Aqua  regia,  154 
Arsenic,  270 

oxides,  272 
Arsiue,  271 
Asbestos,  331 
Atomic  theory,  211 

weights,  213 

determination  of,  215 
Atoms,  211 
Avogadro's  hypothesis,  216 

Barium,  330 

dioxide,  330 

hydroxide,  330 

oxide,  330 

sulphate,  299 
Bases,  122 
Benzene,  178 
Beryllium,  323 
Bismuth,  363 

nitrate,  364 

sulphide,  364 
Bituminous  coal,  170 
Bleaching,  101 

powder,  112,  326 
Blow-pipe.  193 
Boracite,  277 
Borax,  277 
Boron,  276 

crystallized,  277 

oxide,  278 
Brass,  333 
Bromine,  286 
Bunsen  burner,  196,  203 


Burning  in  the  air,  51 
Butane,  177 
Butylene,  177 

Cadmium,  331 
Caesium,  321 
Calamine,  332 
Calcium,  323 

carbonate,  323 

chloride,  324 

hydroxide,  325 

hypochlorite,  326 

oxide,  324 

phosphate,  328 

sulphate,  323,  327 
Calomel,  339 
Carbon,  163 

bisulphide,  268 

dioxide,  180 

in  the  air,  133 

role  irf  nature,  187 

monoxide,  191 
Carbonates,  189,  301 
Carnelian,  282 
Chalk.  323 
Charcoal,  166 

animal,  168 

reduction  by,  174 

wood,  166 
Chemical  affinity,  27 

energy,  56 

work,  56      . 
Chemistry,  2 
Chlorates,  298 
Chlorides,  formation,  287 

properties,  288 
Chlorine,  95 

acids,  116 

bleaching  by,  101 

comparison  with  bromine  and 
iodine,  244 

hydrate,  102 

oxides,  116 
Chromates,  359 
Chrome  alum,  361 

yellow,  361 
Chromic  iron,  359 
Chromium,  359 
Cinnabar,  340 
Clay,  280,  347 
Coal,  170 
Cobalt,  356 


INDEX. 


385 


Columbium,  275 

Combination,  chemical,  laws  of, 

21,  24 

Combining  weights,  24,213 
Combustion,  51 
Compounds,  chemical,  13 
Copper,  335 

alloys,  336 

chlorides,  337 

oxides,  338 

pyrites,  335 

sulphate,  338 

sulphide,  338 
Corrosive  sublimate,  340 
Corundum,  348 
Cryolite,  242,  347 
Crystallography,  249 
Cyanogen,  204 

Decomposition,  heat  of,  55 
Definite  proportions,  law  of,  24 
Diamond,  165 
Dolomite,  331 

Elements,  13,  30,  31,  32 

classification,  232 
Emery,  348 
Epsom  salt,  331 
Ethane,  177 
Ether,  178 
Etbylene,  177,  180 
Eudiometer,  78 

Feldspar,  347 
Ferric  chloride,  353 

hydroxide,  355 
Ferric  oxide,  355 

sulphate,  355 
Ferrous  chloride,  354 

hydroxide,  354 

oxide,  355 

sulphate,  355 
Fire-damp,  179 
Flame,  198 
Fluorine,  242 
Fluor-spar,  242,  323 
Formula,  chemical,  221 

Galenite,  340 

Gases,  combination  by  volume, 

145 
measurement  of,  79 


Gases,  specific  gravity  of,  147 
Gas,  olefiant,  180 
Glass,  329 
Gold,  375 
Graphite,  165 
Granite,  347 
Gunpowder,  310 
Gypsum,  327 

Hematite,  355 

Heat  of  combustion,  54 

decomposition,  55 
Heptane,  177 
Hexane,  177 

Homologous  compounds,  177 
Hornblende,  331 
Hydrocarbons,  176 
Hydrogen,  58 

dioxide,  92 

preparation,  58 

properties,  66 

sulphide,  250 
Hydrosulphides,  256 
Hydroxides,  124,  290 

Iodine,  240 
Iron,  351 

carbonate,  351 

cast,  352 

chlorides,  353 

oxides,  355 

pyrites,  351,  356 

sulphates,  355 

sulphides,  356 

Eaoline,  349 

Kelp,  240 

Kindling  temperature,  52 

Lamp-black,  168 
L?ad,  365 

acetate,  368 

carbonate,  368 

chromate,  361 

nitrate,  368 

oxide,  367 

red  oxide,  367 

sulphate,  368 

sulphide,  368 

white,  368 
Lepidolite,  320 
Lignite,  170 


386 


INDEX. 


Lime,  324 
Litharge,  367 
Lithium,  306 

Magnesia,  332 
Magnesite,  331 
Magnesium,  331 

carbonate,  332 

chloride,  332 

oxide,  332 

sulphate,  332 
Manganese,  357 

dioxide,  357 

oxides,  357 
Marsh  gas,  177,  179 
Marsh's  test,  270 
Mendelejeff' s  periodic  law,  379 
Meerschaum,  331 
Mercuric  chloride,  340 

iodide,  339 

oxide,  339 
Mercurous  chloride,  339 

iodide,  339 
Mercury,  339 

chlorides,  337,  339 

oxide,  339 

sulphide,  340 
Metallic  properties,  285 
Metals,  classification,  284 
Methane,  177,  179 
Mica,  347 
Minium,  367 
Mixture,  mechanical,  13 
Molecular  formulas,  221 

weights,  218 
Molecules,  215,  220 
Mortar,  329 
Multiple  proportions,  26 

Neutralization,  117 
Nickel,  356 
Nitrates,  297 
Nitric  oxide,  158 
Nitrogen,  127 

family,  265 

in  air,  128 

oxides,  156 

pentoxide,  157 

peroxide,  158 

trioxide,  157 
Nitrous  oxide,  157 
Nomenclature,  acids,  128 


Nomenclature,  bases,  124 
salts,  124 

Octane,  177 
Osmium,  373 
Oxides,  57,  290 
Oxygen,  33 

preparation,  33 

properties,  43 
Oxygen  blow-pipe,  86 
Ozone,  91 

in  air,  91 

relation  to  oxygen,  221 

Palladium,  373 
Pentane,  177 
Petroleum,  176 
Phosphates,  303 
Phosphine,  267 
Phosphonium  salts,  267 
Phosphorite,  265 
Phosphorus,  265 

oxides,  268 

red,  266 

Pitchblende,  363 
Plaster  of  Paris,  327 
Platinum,  373 

chloride,  374 
Plumbago,  165 
Potassium,  306 

chlorate*  111,  310 

chromate,  359 

dichromate,  360 

ferrocyanide,  204 

hydroxide,  308 

hypochlorito,  111 

iodide,  308 

mangan.  te  358 

nitrate,  309 

perchlorate,  39 

permanganate,  358 
Propane,  177 
Propylene,  177 

Quartz,  280,  282 
Quartzite,  280,  282 

Respiration,  185 
Rhodium.  373 
Rubidium,  320 
Ruby,  348 
Ruby  copper,  335 


INDEX. 


387 


Ruthenium,  373 

Safety-lamp,  197 
Salts,  122 

decomposition  by  acids,  292 
bases,  293 

acid,  262 

neutral,  262 

nomenclature,  124 

normal,  262 
Sapphire,  348 
Scandium,  382 
Serpentine,  331 
Selenium,  263 
Silica,  282 
Silicates,  303 
Silicon,  280 

fluoride,  281 

oxide,  282 
Silver,  340 

bromide,  343 

chloride,  343 

iodide,  343 

nitrate,  342 
Slow  oxidation,  53 
Soapstone,  331 
Sodium,  311 

borate,  277 

carbonate,  313 

chloride,  311 

hydroxide,  312 

hVposulphite,  263 

nitrate,  312 

phosphate,  316 

sulphate,  313 

thiosulphate,  263 
Solution,  90 
Specific  heat,  344 

relation  to  atomic  weights,  345 
Spectroscope,  320 
Spinel,  349 
Steel,  352 
Stibme,  274 
Strontium,  330 
Sulphates,  298 

formation,  298 

properties,  299 


Sulphides,  294 
Sulphites,  301 
Sulphur,  247 

dimorphism  of,  250 

dioxide,  257 

oxygen  acids,  256 

trioxide.  257 

Tantalum,  275 
Tellurium,  263 
Tin,  369 

dichlonde,  369 

oxides,  370 

sulphides,  371 

tetrachloride,  371 
Toluene,  178 

Ultramarine,  349 
Uranium,  362 
Uranyl  nitrate,  363 
salts,  363 

Valence,  225 
Vanadium,  275 
Vitriol,  blue,  338 

green,  355 

white,  333 

Water,  71 

analysis,  74 
hard,  89,  327 
in  air,  134 

maximum  density,  90 
of  cystallizalion,  72 
solvent  properties,  90 
synthesis  of.  73,  83 
uses  in  laboratory,  90 
Wood-spirit,  178 

Xylene,  178 

Zinc,  332 
chloride,  334 
oxide,  333 
sulphate,  333 
sulphide,  334 


APPABATUS  AND  CHEMICALS. 

WITH  two  or  three  exceptions,  all  the  experiments  de- 
scribed in  this  book  can  be  performed  in  any  chemical  lab- 
oratory. The  apparatus  needed  is  of  the  simplest  kind, 
and  the  chemicals  are  such  as  can  be  obtained  without  dif- 
ficulty. For  the  benefit  of  those  who  have  no  laboratory  at 
command,  and  who  may  wish  to  make  arrangements  for 
going  through  with  the  experimental  work,  the  following 
list  has  been  drawn  up.  In  it  is  included  everything 
necessary  to  perform  the  experiments  on  a  small  scale. 
Should  it  be  desired  to  fit  up  a  room  with  conveniences  for 
students,  the  amount  of  apparatus  necessary  would  depend 
upon  the  number  of  students,  but  for  each  individual  the 
expense  would  be  small,  as  many  of  the  pieces  of  apparatus, 
such  as  the  galvanic  battery,  burette,  weights,  scales,  etc., 
need  not  be  multiplied.  In  place  of  some  of  the  pieces  of 
apparatus  described  in  the  book,  ordinary  kitchen  utensils 
will  answer :  thus,  for  example,  instead  of  the  trough  for 
collecting  gases,  a  tin  pan  or  a  deep  earthenware  dish  may 
be  used  ;  instead  of  the  water-bath,  a  stew-pan,  fitted  with 
two  or  three  different- sized  tin  or  sheet-iron  rings  ;  and  in 
place  of  glass  cylinders  for  working  with  gases,  wide- 
mouthed  cheap  bottles. 


APPARATUS  AND  CHEMICALS. 


389 


23iF~  The  publishers  do  not  deal  in  chemicals  and  apparatus,  nor, 
they  may  as  well  say,  receive  commissions  on  them.  Any  orders 
should  be  sent  direct  -to  the  dealer.  Those  whose  names  are  at  the 
end  of  this  list,  the  publishers  take  the  responsiblity  of  recommend- 
ing as  thoroughly  reliable. 

4  oz.  Potass.  Permangan.,  bottle.ftO  30 
4  oz.  Caust.  Soda,  pur  if.,  bottle. .  25 
4  oz.  Caust.  Ammonia,  bottle.  ...  20 
4  oz.  Ammon.  Chloride,  box.  ...  10 

4  oz.  Metall.  Lead,  box 10 

4  oz.  Ammon.  Nitrate,  bottle  ...      20 
4  oz.  White  Arsenic,  bottle. . 
4  oz.  Fluorspar,  powd.,  box. . 
2  oz.  Potass.  Bromide,  bottle 
1  oz.  Potass.  Iodide,   bottle.. 


APPARATUS. 

12  Test-tubes,  5  in $0  35 

1  Test-tube  Stand 30 

1  Bunsen's  Burner 50 

V±  lb.  Germ.  Glass-tubing 15 

1  Triang.  File,  4^  in 25 

1  Round  File,  5  in 25 

2  Bunsen's  Cells,  pt.,  1.20 2  40 

2  Wire  Clamp  Supports,  75  c 1  50 

1  Porcel.  Mortar  3J4  in.  and  pestle      50 


1  Horseshoe  Magnet,  3  in . .'. 20 

2  Watch-glasses,  2  in 10 

2  Porcel.  Dishes,    1  ea.   2U    and 

3^  in r 40 

1  Iron  Tripod 25 

1  Mohr's  Burette,  25  in  ^  c.c 1  25 

1  Hess.  Crucible,  4  oz 6 

1  Deflagrat;  Spoon 20 

1  Stopper  Retort,  2  oz 30 

6  Florence  Flasks,  1-4  oz.,  15  c.; 

2-6  oz.,  18  c. ;  2-8  oz.  ;  22  c.; 

1-12  oz.,  25  c 1  20 

1  set  Cork  Borers  of  brass,  6;  set.  1  50 

1  Glass  Tube,  12-15  in.  1.,  l-lJ4in. 

bore,  one  end  closed 50 

2  Funnel  Tubes,  assort 40 

1  set  Gramme  Weights,  20.0-0.01, 

in  box 65 

1  pr.  Hand  Scales,  E.  &  A.  3041. .  85 

2  doz.  Assort.  Corks 18 

1  Platin.  Foil,  1J4  in.  square 50 

1  Quire  Filter-paper 35 

1  Measur.  Glass.,  25  c.c 45 

6  inch.  Platin.  Wire 18 

1  Jewellers'  Blowpipe,  8  in 20 

3  ft.  Gas  Rubber  Tubing 40 

2  ft.  Gas  Rubber  for  connect,  ass.  25 

CHEMICALS. 

^  lb.  Roll  Sulphur,  in  box 10 

4  oz.  Granul.  Tin,  in  box 15 

4  oz.  Potass.  Chlorate,  in  box. . . .  12 

1  lb.  Mangan.  Dioxide,  in  box 15 

1  oz.  Phosphorus,  in  bottle 20 

1  drm.  Sodium,  in  bottle 15 

1  drm.  Potassium,  in  bottle 52 

1  lb.  Granul.  Zinc 25 


*&  lb.  Iron  Sulphide,  box 

2  oz.  Lead  Nitrate,  box 


1  oz.  Red  Phosphorus,  bottle. 
4  oz.  Caust.  Potassa,  bottle. 

4  oz.  Met.  Antimony,  box 

2  oz.  Tar  tar  Emetic,  powd.,  bottle 

4  oz.  Borax,  box 

4  oz.  Fine  Iron  Filings,  box 

4  oz.  Carbon  Disulphide,  bottle.. 
8  oz.  Hydrochlor.  Acid,  bottle... 
8  oz.  Nitric  Acid,  bottle 

1  lb.  Sulphuric  Acid,  bottle 

8  oz.  Copperf oil 

^  drm.  Magnesium  Ribbon 

4  oz.  Magnesium  Sulphate,  box. . 

2  oz.  Barium  Chloride,  box 

1  oz.  Iodine,  gl.  st.  bottle 

2  oz.  Strontium  Nitrate,  bottle. . 

4  oz.  Potass.  Sulphate,  box 

1  oz.  Litmus,  box 

1  Sheet  each  Blue  and  Red  Lit- 

mus paper 

4  oz.  Sodium  Carbon.  Anhydr., 

purif .,  box 

4  oz.  Bleach.  Powder,  bottle 

4  oz.  Ammon.  Carbonate,  bottle. 

2  oz.  Sodium  Phosphate  Cryst.. 

bottle 


2  oz.  Mercury,  bottle 15 

4  oz.  Alum,  box 10 

4  oz.  Potass.  Dichromate,  box. . .  10 

1  oz.  Metall.  Bismuth,  box 25 

4  oz.  Minium,  box 10 

4  oz.  Litharge,  box 10 

1  oz.  Lead  Peroxide,  comm.  bot.  15 
4  oz.  Copper  Sulphate,  box 10 

2  Boxes,  and  delivered  free  on 

board,  N,  Y.  City 1  00 


4  oz.  Calcin.  Gypsum,  box 10 

4  oz.  Sodium  Sulphate,  in  box. . .      10 

4  oz.  Calcium  Choride,  bottle 15  $26  70 

Messrs.  Eimer  &  Amend,  Nos.  205  to  211  Third  Avenue,  New 
York,  will  furnish  the  above  set  at  a  discount  of  5  percent,  or  3  sets 
at  a  discount  of  10  per  cent. 

Any  items  less  than  the  whole  set  will  be  furnished  at  list  price, 
plus  a  small  charge  for  packing.  It  should  be  realized,  however, 
that  usually  the  charge  for  packing  one  article  must  be  as  large  as 
for  several.  Some  of  the  articles  can,  of  course,  be  mailed  without 
any  charge  for  packing. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


MOV  5* 


MAR    18  1943 


LD  21-95w-7,'37 


1 


UNIVERSITY  OF  CALIFOtKIA 


